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 $52.81   6.707%   $56.352   $56.35   $56.35   $56.40  
  Purchase #2 $102.49   10.387%   $113.1356   $113.14   $113.15   $113.10  
  Purchase #3 $25.99   11.110%   $28.8775   $28.88   $28.90   $28.90  
  Purchase #4 $76.53   9.496%   $83.7973   $83.80   $83.80   $83.80  
  Purchase #5 $181.80   7.243%   $194.9678   $194.97   $194.95   $195.00  
  Purchase #6 $203.41   11.748%   $227.3066   $227.31   $227.30   $227.30  
  Purchase #7 $54.73   9.329%   $59.8358   $59.84   $59.85   $59.80  
  7 purchase totals = $697.76       $764.2726   $764.29   $764.30   $764.30