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 $89.50   7.314%   $96.046   $96.05   $96.05   $96.00  
  Purchase #2 $53.79   13.846%   $61.2378   $61.24   $61.25   $61.20  
  Purchase #3 $205.75   5.430%   $216.9222   $216.92   $216.90   $216.90  
  Purchase #4 $157.42   5.787%   $166.5299   $166.53   $166.55   $166.50  
  Purchase #5 $244.35   7.624%   $262.9792   $262.98   $263.00   $263.00  
  Purchase #6 $174.31   8.793%   $189.6371   $189.64   $189.65   $189.60  
  Purchase #7 $131.55   11.141%   $146.206   $146.21   $146.20   $146.20  
  7 purchase totals = $1,056.67       $1,139.5582   $1,139.57   $1,139.60   $1,139.40