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 $39.72   11.711%   $44.3716   $44.37   $44.35   $44.40  
  Purchase #2 $103.27   4.871%   $108.3003   $108.30   $108.30   $108.30  
  Purchase #3 $105.50   10.676%   $116.7632   $116.76   $116.75   $116.80  
  Purchase #4 $158.62   10.565%   $175.3782   $175.38   $175.40   $175.40  
  Purchase #5 $233.88   6.484%   $249.0448   $249.04   $249.05   $249.00  
  Purchase #6 $210.38   10.365%   $232.1859   $232.19   $232.20   $232.20  
  Purchase #7 $120.33   10.836%   $133.369   $133.37   $133.35   $133.40  
  7 purchase totals = $971.70       $1,059.4130   $1,059.41   $1,059.40   $1,059.50