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 $60.57   3.499%   $62.6893   $62.69   $62.70   $62.70  
  Purchase #2 $140.68   13.699%   $159.9518   $159.95   $159.95   $160.00  
  Purchase #3 $219.43   4.287%   $228.837   $228.84   $228.85   $228.80  
  Purchase #4 $26.65   8.652%   $28.9558   $28.96   $28.95   $29.00  
  Purchase #5 $75.34   13.463%   $85.483   $85.48   $85.50   $85.50  
  Purchase #6 $184.79   5.318%   $194.6171   $194.62   $194.60   $194.60  
  Purchase #7 $232.62   10.721%   $257.5592   $257.56   $257.55   $257.60  
  7 purchase totals = $940.08       $1,018.0932   $1,018.10   $1,018.10   $1,018.20