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 $198.28   8.657%   $215.4451   $215.45   $215.45   $215.40  
  Purchase #2 $61.77   10.421%   $68.2071   $68.21   $68.20   $68.20  
  Purchase #3 $33.83   3.562%   $35.035   $35.04   $35.05   $35.00  
  Purchase #4 $180.35   8.662%   $195.9719   $195.97   $195.95   $196.00  
  Purchase #5 $23.35   12.834%   $26.3467   $26.35   $26.35   $26.30  
  Purchase #6 $44.73   12.465%   $50.3056   $50.31   $50.30   $50.30  
  Purchase #7 $205.81   9.592%   $225.5513   $225.55   $225.55   $225.60  
  7 purchase totals = $748.12       $816.8627   $816.88   $816.85   $816.80