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 $243.67   7.158%   $261.1119   $261.11   $261.10   $261.10  
  Purchase #2 $87.52   10.325%   $96.5564   $96.56   $96.55   $96.60  
  Purchase #3 $67.75   11.627%   $75.6273   $75.63   $75.65   $75.60  
  Purchase #4 $31.44   7.291%   $33.7323   $33.73   $33.75   $33.70  
  Purchase #5 $169.86   10.852%   $188.2932   $188.29   $188.30   $188.30  
  Purchase #6 $120.93   4.252%   $126.0719   $126.07   $126.05   $126.10  
  Purchase #7 $108.66   4.213%   $113.2378   $113.24   $113.25   $113.20  
  7 purchase totals = $829.83       $894.6308   $894.63   $894.65   $894.60