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 $206.51   13.203%   $233.7755   $233.78   $233.80   $233.80  
  Purchase #2 $196.30   3.437%   $203.0468   $203.05   $203.05   $203.00  
  Purchase #3 $209.51   11.793%   $234.2175   $234.22   $234.20   $234.20  
  Purchase #4 $193.68   3.323%   $200.116   $200.12   $200.10   $200.10  
  Purchase #5 $82.26   12.643%   $92.6601   $92.66   $92.65   $92.70  
  Purchase #6 $237.53   5.156%   $249.777   $249.78   $249.80   $249.80  
  Purchase #7 $136.98   13.511%   $155.4874   $155.49   $155.50   $155.50  
  7 purchase totals = $1,262.77       $1,369.0803   $1,369.10   $1,369.10   $1,369.10