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 $201.89   11.551%   $225.2103   $225.21   $225.20   $225.20  
  Purchase #2 $226.48   8.579%   $245.9097   $245.91   $245.90   $245.90  
  Purchase #3 $48.80   9.700%   $53.5336   $53.53   $53.55   $53.50  
  Purchase #4 $12.80   12.165%   $14.3571   $14.36   $14.35   $14.40  
  Purchase #5 $93.59   12.267%   $105.0707   $105.07   $105.05   $105.10  
  Purchase #6 $40.84   10.353%   $45.0682   $45.07   $45.05   $45.10  
  Purchase #7 $20.43   11.653%   $22.8107   $22.81   $22.80   $22.80  
  7 purchase totals = $644.83       $711.9603   $711.96   $711.90   $712.00