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 $136.98   13.714%   $155.7654   $155.77   $155.75   $155.80  
  Purchase #2 $150.47   9.616%   $164.9392   $164.94   $164.95   $164.90  
  Purchase #3 $38.42   12.449%   $43.2029   $43.20   $43.20   $43.20  
  Purchase #4 $94.82   10.286%   $104.5732   $104.57   $104.55   $104.60  
  Purchase #5 $235.29   11.603%   $262.5907   $262.59   $262.60   $262.60  
  Purchase #6 $167.93   11.425%   $187.116   $187.12   $187.10   $187.10  
  Purchase #7 $21.26   9.306%   $23.2385   $23.24   $23.25   $23.20  
  7 purchase totals = $845.17       $941.4259   $941.43   $941.40   $941.40