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 $209.46   11.819%   $234.2161   $234.22   $234.20   $234.20  
  Purchase #2 $173.64   12.829%   $195.9163   $195.92   $195.90   $195.90  
  Purchase #3 $15.99   6.215%   $16.9838   $16.98   $17.00   $17.00  
  Purchase #4 $185.41   4.735%   $194.1892   $194.19   $194.20   $194.20  
  Purchase #5 $172.93   9.541%   $189.4293   $189.43   $189.45   $189.40  
  Purchase #6 $72.57   7.758%   $78.2   $78.20   $78.20   $78.20  
  Purchase #7 $144.27   9.434%   $157.8804   $157.88   $157.90   $157.90  
  7 purchase totals = $974.27       $1,066.8151   $1,066.82   $1,066.85   $1,066.80