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 $236.86   7.344%   $254.255   $254.26   $254.25   $254.30  
  Purchase #2 $54.74   11.517%   $61.0444   $61.04   $61.05   $61.00  
  Purchase #3 $152.40   9.109%   $166.2821   $166.28   $166.30   $166.30  
  Purchase #4 $8.68   9.213%   $9.4797   $9.48   $9.50   $9.50  
  Purchase #5 $49.55   7.752%   $53.3911   $53.39   $53.40   $53.40  
  Purchase #6 $57.38   3.479%   $59.3763   $59.38   $59.40   $59.40  
  Purchase #7 $187.67   7.215%   $201.2104   $201.21   $201.20   $201.20  
  7 purchase totals = $747.28       $805.0390   $805.04   $805.10   $805.10