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 $85.33   11.222%   $94.9057   $94.91   $94.90   $94.90  
  Purchase #2 $88.37   9.340%   $96.6238   $96.62   $96.60   $96.60  
  Purchase #3 $127.42   8.648%   $138.4393   $138.44   $138.45   $138.40  
  Purchase #4 $49.62   10.771%   $54.9646   $54.96   $54.95   $55.00  
  Purchase #5 $47.79   12.378%   $53.7054   $53.71   $53.70   $53.70  
  Purchase #6 $220.74   11.551%   $246.2377   $246.24   $246.25   $246.20  
  Purchase #7 $91.55   9.681%   $100.413   $100.41   $100.40   $100.40  
  7 purchase totals = $710.82       $785.2895   $785.29   $785.25   $785.20