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 $32.67   4.197%   $34.0412   $34.04   $34.05   $34.00  
  Purchase #2 $62.60   10.382%   $69.0991   $69.10   $69.10   $69.10  
  Purchase #3 $174.59   4.811%   $182.9895   $182.99   $183.00   $183.00  
  Purchase #4 $246.49   11.686%   $275.2948   $275.29   $275.30   $275.30  
  Purchase #5 $19.30   6.191%   $20.4949   $20.49   $20.50   $20.50  
  Purchase #6 $200.48   12.865%   $226.2718   $226.27   $226.25   $226.30  
  Purchase #7 $51.57   4.213%   $53.7426   $53.74   $53.75   $53.70  
  7 purchase totals = $787.70       $861.9339   $861.92   $861.95   $861.90