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 $119.52   4.747%   $125.1936   $125.19   $125.20   $125.20  
  Purchase #2 $109.66   10.419%   $121.0855   $121.09   $121.10   $121.10  
  Purchase #3 $190.72   5.257%   $200.7462   $200.75   $200.75   $200.70  
  Purchase #4 $52.99   13.463%   $60.124   $60.12   $60.10   $60.10  
  Purchase #5 $20.67   7.783%   $22.2787   $22.28   $22.30   $22.30  
  Purchase #6 $140.84   9.259%   $153.8804   $153.88   $153.90   $153.90  
  Purchase #7 $161.48   10.549%   $178.5145   $178.51   $178.50   $178.50  
  7 purchase totals = $795.88       $861.8229   $861.82   $861.85   $861.80