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 $226.60   8.344%   $245.5075   $245.51   $245.50   $245.50  
  Purchase #2 $158.97   8.491%   $172.4681   $172.47   $172.45   $172.50  
  Purchase #3 $144.88   9.690%   $158.9189   $158.92   $158.90   $158.90  
  Purchase #4 $29.88   8.544%   $32.4329   $32.43   $32.45   $32.40  
  Purchase #5 $214.97   9.608%   $235.6243   $235.62   $235.60   $235.60  
  Purchase #6 $52.50   6.526%   $55.9262   $55.93   $55.95   $55.90  
  Purchase #7 $182.85   7.749%   $197.019   $197.02   $197.00   $197.00  
  7 purchase totals = $1,010.65       $1,097.8969   $1,097.90   $1,097.85   $1,097.80