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 $187.48   11.164%   $208.4103   $208.41   $208.40   $208.40  
  Purchase #2 $240.54   8.282%   $260.4615   $260.46   $260.45   $260.50  
  Purchase #3 $27.45   12.119%   $30.7767   $30.78   $30.80   $30.80  
  Purchase #4 $48.65   12.694%   $54.8256   $54.83   $54.85   $54.80  
  Purchase #5 $247.91   6.562%   $264.1779   $264.18   $264.20   $264.20  
  Purchase #6 $176.49   9.570%   $193.3801   $193.38   $193.40   $193.40  
  Purchase #7 $82.47   6.605%   $87.9171   $87.92   $87.90   $87.90  
  7 purchase totals = $1,010.99       $1,099.9492   $1,099.96   $1,100.00   $1,100.00