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 $23.86   3.117%   $24.6037   $24.60   $24.60   $24.60  
  Purchase #2 $126.49   4.331%   $131.9683   $131.97   $131.95   $132.00  
  Purchase #3 $104.92   7.393%   $112.6767   $112.68   $112.70   $112.70  
  Purchase #4 $146.40   6.278%   $155.591   $155.59   $155.60   $155.60  
  Purchase #5 $19.36   5.334%   $20.3927   $20.39   $20.40   $20.40  
  Purchase #6 $233.35   13.282%   $264.3435   $264.34   $264.35   $264.30  
  Purchase #7 $167.87   10.106%   $184.8349   $184.83   $184.85   $184.80  
  7 purchase totals = $822.25       $894.4108   $894.40   $894.45   $894.40