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 $137.68   10.117%   $151.6091   $151.61   $151.60   $151.60  
  Purchase #2 $148.41   11.820%   $165.9521   $165.95   $165.95   $166.00  
  Purchase #3 $249.30   8.540%   $270.5902   $270.59   $270.60   $270.60  
  Purchase #4 $208.39   8.567%   $226.2428   $226.24   $226.25   $226.20  
  Purchase #5 $64.65   3.558%   $66.9502   $66.95   $66.95   $67.00  
  Purchase #6 $249.97   8.453%   $271.1   $271.10   $271.10   $271.10  
  Purchase #7 $60.48   10.456%   $66.8038   $66.80   $66.80   $66.80  
  7 purchase totals = $1,118.88       $1,219.2482   $1,219.24   $1,219.25   $1,219.30