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 $81.77   11.646%   $91.2929   $91.29   $91.30   $91.30  
  Purchase #2 $159.76   5.170%   $168.0196   $168.02   $168.00   $168.00  
  Purchase #3 $92.96   3.709%   $96.4079   $96.41   $96.40   $96.40  
  Purchase #4 $185.77   9.782%   $203.942   $203.94   $203.95   $203.90  
  Purchase #5 $200.75   6.329%   $213.4555   $213.46   $213.45   $213.50  
  Purchase #6 $125.25   5.102%   $131.6403   $131.64   $131.65   $131.60  
  Purchase #7 $146.35   5.356%   $154.1885   $154.19   $154.20   $154.20  
  7 purchase totals = $992.61       $1,058.9467   $1,058.95   $1,058.95   $1,058.90