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 $203.49   5.275%   $214.2241   $214.22   $214.20   $214.20  
  Purchase #2 $214.30   12.342%   $240.7489   $240.75   $240.75   $240.70  
  Purchase #3 $76.64   4.815%   $80.3302   $80.33   $80.35   $80.30  
  Purchase #4 $46.45   8.277%   $50.2947   $50.29   $50.30   $50.30  
  Purchase #5 $111.53   13.841%   $126.9669   $126.97   $126.95   $127.00  
  Purchase #6 $74.98   10.702%   $83.0044   $83.00   $83.00   $83.00  
  Purchase #7 $166.97   4.165%   $173.9243   $173.92   $173.90   $173.90  
  7 purchase totals = $894.36       $969.4935   $969.48   $969.45   $969.40