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 $213.28   5.281%   $224.5433   $224.54   $224.55   $224.50  
  Purchase #2 $61.97   11.286%   $68.9639   $68.96   $68.95   $69.00  
  Purchase #3 $98.86   10.786%   $109.523   $109.52   $109.50   $109.50  
  Purchase #4 $139.35   11.330%   $155.1384   $155.14   $155.15   $155.10  
  Purchase #5 $247.47   5.180%   $260.2889   $260.29   $260.30   $260.30  
  Purchase #6 $234.40   6.640%   $249.9642   $249.96   $249.95   $250.00  
  Purchase #7 $233.63   7.853%   $251.977   $251.98   $252.00   $252.00  
  7 purchase totals = $1,228.96       $1,320.3987   $1,320.39   $1,320.40   $1,320.40