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 $48.67   9.272%   $53.1827   $53.18   $53.20   $53.20  
  Purchase #2 $205.31   13.473%   $232.9714   $232.97   $232.95   $233.00  
  Purchase #3 $250.68   12.236%   $281.3532   $281.35   $281.35   $281.40  
  Purchase #4 $83.56   12.571%   $94.0643   $94.06   $94.05   $94.10  
  Purchase #5 $73.37   11.765%   $82.002   $82.00   $82.00   $82.00  
  Purchase #6 $129.43   3.388%   $133.8151   $133.82   $133.80   $133.80  
  Purchase #7 $133.72   11.365%   $148.9173   $148.92   $148.90   $148.90  
  7 purchase totals = $924.74       $1,026.3060   $1,026.30   $1,026.25   $1,026.40