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 $228.26   11.574%   $254.6788   $254.68   $254.70   $254.70  
  Purchase #2 $184.39   3.422%   $190.6998   $190.70   $190.70   $190.70  
  Purchase #3 $62.91   4.139%   $65.5138   $65.51   $65.50   $65.50  
  Purchase #4 $81.65   3.719%   $84.6866   $84.69   $84.70   $84.70  
  Purchase #5 $246.85   3.850%   $256.3537   $256.35   $256.35   $256.40  
  Purchase #6 $187.46   4.134%   $195.2096   $195.21   $195.20   $195.20  
  Purchase #7 $34.74   12.697%   $39.1509   $39.15   $39.15   $39.20  
  7 purchase totals = $1,026.26       $1,086.2932   $1,086.29   $1,086.30   $1,086.40