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 $86.36   8.470%   $93.6747   $93.67   $93.65   $93.70  
  Purchase #2 $217.98   8.357%   $236.1966   $236.20   $236.20   $236.20  
  Purchase #3 $180.80   12.103%   $202.6822   $202.68   $202.70   $202.70  
  Purchase #4 $231.47   11.283%   $257.5868   $257.59   $257.60   $257.60  
  Purchase #5 $53.91   8.319%   $58.3948   $58.39   $58.40   $58.40  
  Purchase #6 $60.53   8.423%   $65.6284   $65.63   $65.65   $65.60  
  Purchase #7 $92.31   9.788%   $101.3453   $101.35   $101.35   $101.30  
  7 purchase totals = $923.36       $1,015.5088   $1,015.51   $1,015.55   $1,015.50