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 $67.79   12.456%   $76.2339   $76.23   $76.25   $76.20  
  Purchase #2 $78.39   10.384%   $86.53   $86.53   $86.55   $86.50  
  Purchase #3 $231.77   8.102%   $250.548   $250.55   $250.55   $250.50  
  Purchase #4 $85.72   6.672%   $91.4392   $91.44   $91.45   $91.40  
  Purchase #5 $124.26   3.155%   $128.1804   $128.18   $128.20   $128.20  
  Purchase #6 $130.54   11.242%   $145.2153   $145.22   $145.20   $145.20  
  Purchase #7 $225.60   9.218%   $246.3958   $246.40   $246.40   $246.40  
  7 purchase totals = $944.07       $1,024.5426   $1,024.55   $1,024.60   $1,024.40