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 $68.92   9.488%   $75.4591   $75.46   $75.45   $75.50  
  Purchase #2 $125.28   3.648%   $129.8502   $129.85   $129.85   $129.90  
  Purchase #3 $174.79   12.846%   $197.2435   $197.24   $197.25   $197.20  
  Purchase #4 $105.62   9.855%   $116.0289   $116.03   $116.05   $116.00  
  Purchase #5 $31.28   4.658%   $32.737   $32.74   $32.75   $32.70  
  Purchase #6 $177.74   7.426%   $190.939   $190.94   $190.95   $190.90  
  Purchase #7 $19.49   11.355%   $21.7031   $21.70   $21.70   $21.70  
  7 purchase totals = $703.12       $763.9608   $763.96   $764.00   $763.90