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 $63.29   13.632%   $71.9177   $71.92   $71.90   $71.90  
  Purchase #2 $238.94   13.742%   $271.7751   $271.78   $271.80   $271.80  
  Purchase #3 $49.85   5.807%   $52.7448   $52.74   $52.75   $52.70  
  Purchase #4 $160.56   12.191%   $180.1339   $180.13   $180.15   $180.10  
  Purchase #5 $162.84   6.245%   $173.0094   $173.01   $173.00   $173.00  
  Purchase #6 $61.93   3.145%   $63.8777   $63.88   $63.90   $63.90  
  Purchase #7 $38.64   6.547%   $41.1698   $41.17   $41.15   $41.20  
  7 purchase totals = $776.05       $854.6284   $854.63   $854.65   $854.60