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 $116.95   6.134%   $124.1237   $124.12   $124.10   $124.10  
  Purchase #2 $126.58   8.324%   $137.1165   $137.12   $137.10   $137.10  
  Purchase #3 $183.28   9.851%   $201.3349   $201.33   $201.35   $201.30  
  Purchase #4 $146.42   8.644%   $159.0765   $159.08   $159.10   $159.10  
  Purchase #5 $11.83   6.726%   $12.6257   $12.63   $12.65   $12.60  
  Purchase #6 $206.50   9.121%   $225.3349   $225.33   $225.35   $225.30  
  Purchase #7 $160.65   9.409%   $175.7656   $175.77   $175.75   $175.80  
  7 purchase totals = $952.21       $1,035.3778   $1,035.38   $1,035.40   $1,035.30