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 $238.98   12.173%   $268.071   $268.07   $268.05   $268.10  
  Purchase #2 $122.70   4.782%   $128.5675   $128.57   $128.55   $128.60  
  Purchase #3 $188.65   3.485%   $195.2245   $195.22   $195.20   $195.20  
  Purchase #4 $115.49   8.793%   $125.645   $125.65   $125.65   $125.60  
  Purchase #5 $118.31   4.792%   $123.9794   $123.98   $124.00   $124.00  
  Purchase #6 $54.90   12.328%   $61.6681   $61.67   $61.65   $61.70  
  Purchase #7 $104.42   4.793%   $109.4249   $109.42   $109.40   $109.40  
  7 purchase totals = $943.45       $1,012.5804   $1,012.58   $1,012.50   $1,012.60