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 $195.25   10.646%   $216.0363   $216.04   $216.05   $216.00  
  Purchase #2 $107.98   7.465%   $116.0407   $116.04   $116.05   $116.00  
  Purchase #3 $158.75   11.402%   $176.8507   $176.85   $176.85   $176.90  
  Purchase #4 $91.46   5.361%   $96.3632   $96.36   $96.35   $96.40  
  Purchase #5 $90.54   12.367%   $101.7371   $101.74   $101.75   $101.70  
  Purchase #6 $64.49   12.261%   $72.3971   $72.40   $72.40   $72.40  
  Purchase #7 $211.65   5.357%   $222.9881   $222.99   $223.00   $223.00  
  7 purchase totals = $920.12       $1,002.4132   $1,002.42   $1,002.45   $1,002.40