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 $129.29   13.666%   $146.9588   $146.96   $146.95   $147.00  
  Purchase #2 $202.60   12.508%   $227.9412   $227.94   $227.95   $227.90  
  Purchase #3 $144.53   10.770%   $160.0959   $160.10   $160.10   $160.10  
  Purchase #4 $238.44   4.538%   $249.2604   $249.26   $249.25   $249.30  
  Purchase #5 $73.98   12.257%   $83.0477   $83.05   $83.05   $83.00  
  Purchase #6 $82.89   5.175%   $87.1796   $87.18   $87.20   $87.20  
  Purchase #7 $57.30   4.407%   $59.8252   $59.83   $59.85   $59.80  
  7 purchase totals = $929.03       $1,014.3088   $1,014.32   $1,014.35   $1,014.30