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 $68.94   9.317%   $75.3631   $75.36   $75.35   $75.40  
  Purchase #2 $40.73   8.796%   $44.3126   $44.31   $44.30   $44.30  
  Purchase #3 $184.42   11.832%   $206.2406   $206.24   $206.25   $206.20  
  Purchase #4 $223.35   9.581%   $244.7492   $244.75   $244.75   $244.70  
  Purchase #5 $69.30   5.843%   $73.3492   $73.35   $73.35   $73.30  
  Purchase #6 $225.51   4.635%   $235.9624   $235.96   $235.95   $236.00  
  Purchase #7 $121.73   13.456%   $138.11   $138.11   $138.10   $138.10  
  7 purchase totals = $933.98       $1,018.0871   $1,018.08   $1,018.05   $1,018.00