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 $228.98   9.729%   $251.2575   $251.26   $251.25   $251.30  
  Purchase #2 $203.97   9.339%   $223.0188   $223.02   $223.00   $223.00  
  Purchase #3 $242.30   11.114%   $269.2292   $269.23   $269.25   $269.20  
  Purchase #4 $68.61   7.847%   $73.9938   $73.99   $74.00   $74.00  
  Purchase #5 $119.95   11.222%   $133.4108   $133.41   $133.40   $133.40  
  Purchase #6 $152.45   4.643%   $159.5283   $159.53   $159.55   $159.50  
  Purchase #7 $56.27   8.598%   $61.1081   $61.11   $61.10   $61.10  
  7 purchase totals = $1,072.53       $1,171.5465   $1,171.55   $1,171.55   $1,171.50