Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $182.58   6.126%   $193.7649   $193.76   $193.75   $193.80  
  Purchase #2 $187.26   8.684%   $203.5217   $203.52   $203.50   $203.50  
  Purchase #3 $149.70   4.737%   $156.7913   $156.79   $156.80   $156.80  
  Purchase #4 $213.83   5.518%   $225.6291   $225.63   $225.65   $225.60  
  Purchase #5 $112.31   12.382%   $126.2162   $126.22   $126.20   $126.20  
  Purchase #6 $162.38   12.129%   $182.0751   $182.08   $182.10   $182.10  
  Purchase #7 $151.85   5.164%   $159.6915   $159.69   $159.70   $159.70  
  7 purchase totals = $1,159.91       $1,247.6898   $1,247.69   $1,247.70   $1,247.70