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 $232.85   8.212%   $251.9716   $251.97   $251.95   $252.00  
  Purchase #2 $57.42   7.406%   $61.6725   $61.67   $61.65   $61.70  
  Purchase #3 $178.30   5.864%   $188.7555   $188.76   $188.75   $188.80  
  Purchase #4 $204.67   4.157%   $213.1781   $213.18   $213.20   $213.20  
  Purchase #5 $51.59   11.353%   $57.447   $57.45   $57.45   $57.40  
  Purchase #6 $225.43   6.150%   $239.2939   $239.29   $239.30   $239.30  
  Purchase #7 $46.62   9.448%   $51.0247   $51.02   $51.00   $51.00  
  7 purchase totals = $996.88       $1,063.3433   $1,063.34   $1,063.30   $1,063.40