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 $206.86   11.546%   $230.7441   $230.74   $230.75   $230.70  
  Purchase #2 $235.52   8.250%   $254.9504   $254.95   $254.95   $255.00  
  Purchase #3 $95.34   11.555%   $106.3565   $106.36   $106.35   $106.40  
  Purchase #4 $130.30   7.636%   $140.2497   $140.25   $140.25   $140.20  
  Purchase #5 $22.84   7.407%   $24.5318   $24.53   $24.55   $24.50  
  Purchase #6 $195.55   13.752%   $222.442   $222.44   $222.45   $222.40  
  Purchase #7 $242.61   5.672%   $256.3708   $256.37   $256.35   $256.40  
  7 purchase totals = $1,129.02       $1,235.6453   $1,235.64   $1,235.65   $1,235.60