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 $193.71   5.330%   $204.0347   $204.03   $204.05   $204.00  
  Purchase #2 $128.40   7.703%   $138.2907   $138.29   $138.30   $138.30  
  Purchase #3 $73.44   7.734%   $79.1198   $79.12   $79.10   $79.10  
  Purchase #4 $220.53   9.383%   $241.2223   $241.22   $241.20   $241.20  
  Purchase #5 $60.40   3.268%   $62.3739   $62.37   $62.35   $62.40  
  Purchase #6 $141.90   7.860%   $153.0533   $153.05   $153.05   $153.10  
  Purchase #7 $65.72   8.115%   $71.0532   $71.05   $71.05   $71.10  
  7 purchase totals = $884.10       $949.1479   $949.13   $949.10   $949.20