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 $64.46   8.732%   $70.0886   $70.09   $70.10   $70.10  
  Purchase #2 $218.83   7.364%   $234.9446   $234.94   $234.95   $234.90  
  Purchase #3 $57.31   11.786%   $64.0646   $64.06   $64.05   $64.10  
  Purchase #4 $29.87   10.688%   $33.0625   $33.06   $33.05   $33.10  
  Purchase #5 $125.59   3.356%   $129.8048   $129.80   $129.80   $129.80  
  Purchase #6 $37.58   7.757%   $40.4951   $40.50   $40.50   $40.50  
  Purchase #7 $197.79   11.553%   $220.6407   $220.64   $220.65   $220.60  
  7 purchase totals = $731.43       $793.1009   $793.09   $793.10   $793.10