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 $205.92   10.222%   $226.9691   $226.97   $226.95   $227.00  
  Purchase #2 $99.78   5.859%   $105.6261   $105.63   $105.65   $105.60  
  Purchase #3 $166.31   13.702%   $189.0978   $189.10   $189.10   $189.10  
  Purchase #4 $30.28   4.460%   $31.6305   $31.63   $31.65   $31.60  
  Purchase #5 $143.82   11.269%   $160.0271   $160.03   $160.05   $160.00  
  Purchase #6 $200.99   5.453%   $211.95   $211.95   $211.95   $212.00  
  Purchase #7 $193.85   6.485%   $206.4212   $206.42   $206.40   $206.40  
  7 purchase totals = $1,040.95       $1,131.7218   $1,131.73   $1,131.75   $1,131.70