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 $118.94   4.504%   $124.2971   $124.30   $124.30   $124.30  
  Purchase #2 $168.67   8.301%   $182.6713   $182.67   $182.65   $182.70  
  Purchase #3 $144.85   6.799%   $154.6984   $154.70   $154.70   $154.70  
  Purchase #4 $146.91   5.674%   $155.2457   $155.25   $155.25   $155.20  
  Purchase #5 $190.95   5.673%   $201.7826   $201.78   $201.80   $201.80  
  Purchase #6 $142.72   7.761%   $153.7965   $153.80   $153.80   $153.80  
  Purchase #7 $248.53   12.452%   $279.477   $279.48   $279.50   $279.50  
  7 purchase totals = $1,161.57       $1,251.9686   $1,251.98   $1,252.00   $1,252.00