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 $94.53   10.867%   $104.8026   $104.80   $104.80   $104.80  
  Purchase #2 $162.67   3.515%   $168.3879   $168.39   $168.40   $168.40  
  Purchase #3 $215.63   3.832%   $223.8929   $223.89   $223.90   $223.90  
  Purchase #4 $54.56   11.809%   $61.003   $61.00   $61.00   $61.00  
  Purchase #5 $236.37   12.456%   $265.8122   $265.81   $265.80   $265.80  
  Purchase #6 $238.65   9.265%   $260.7609   $260.76   $260.75   $260.80  
  Purchase #7 $46.43   10.236%   $51.1826   $51.18   $51.20   $51.20  
  7 purchase totals = $1,048.84       $1,135.8421   $1,135.83   $1,135.85   $1,135.90