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 $113.41   9.386%   $124.0547   $124.05   $124.05   $124.10  
  Purchase #2 $210.87   11.257%   $234.6076   $234.61   $234.60   $234.60  
  Purchase #3 $186.79   5.208%   $196.518   $196.52   $196.50   $196.50  
  Purchase #4 $47.81   11.199%   $53.1642   $53.16   $53.15   $53.20  
  Purchase #5 $21.74   12.168%   $24.3853   $24.39   $24.40   $24.40  
  Purchase #6 $139.97   8.819%   $152.314   $152.31   $152.30   $152.30  
  Purchase #7 $170.29   4.543%   $178.0263   $178.03   $178.05   $178.00  
  7 purchase totals = $890.88       $963.0701   $963.07   $963.05   $963.10