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 $135.39   13.614%   $153.822   $153.82   $153.80   $153.80  
  Purchase #2 $35.39   5.762%   $37.4292   $37.43   $37.45   $37.40  
  Purchase #3 $245.52   5.746%   $259.6276   $259.63   $259.65   $259.60  
  Purchase #4 $195.90   5.617%   $206.9037   $206.90   $206.90   $206.90  
  Purchase #5 $216.34   7.769%   $233.1475   $233.15   $233.15   $233.10  
  Purchase #6 $170.81   13.294%   $193.5175   $193.52   $193.50   $193.50  
  Purchase #7 $15.72   11.438%   $17.5181   $17.52   $17.50   $17.50  
  7 purchase totals = $1,015.07       $1,101.9656   $1,101.97   $1,101.95   $1,101.80