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 $154.60   7.873%   $166.7717   $166.77   $166.75   $166.80  
  Purchase #2 $229.94   4.837%   $241.0622   $241.06   $241.05   $241.10  
  Purchase #3 $68.57   9.613%   $75.1616   $75.16   $75.15   $75.20  
  Purchase #4 $119.85   4.601%   $125.3643   $125.36   $125.35   $125.40  
  Purchase #5 $22.78   13.748%   $25.9118   $25.91   $25.90   $25.90  
  Purchase #6 $212.74   11.325%   $236.8328   $236.83   $236.85   $236.80  
  Purchase #7 $66.93   13.248%   $75.7969   $75.80   $75.80   $75.80  
  7 purchase totals = $875.41       $946.9013   $946.89   $946.85   $947.00