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 $188.42   3.864%   $195.7005   $195.70   $195.70   $195.70  
  Purchase #2 $22.62   7.525%   $24.3222   $24.32   $24.30   $24.30  
  Purchase #3 $41.81   6.165%   $44.3876   $44.39   $44.40   $44.40  
  Purchase #4 $24.46   13.714%   $27.8144   $27.81   $27.80   $27.80  
  Purchase #5 $246.30   13.284%   $279.0185   $279.02   $279.00   $279.00  
  Purchase #6 $69.71   10.780%   $77.2247   $77.22   $77.20   $77.20  
  Purchase #7 $118.96   5.607%   $125.6301   $125.63   $125.65   $125.60  
  7 purchase totals = $712.28       $774.0980   $774.09   $774.05   $774.00