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 $70.74   9.598%   $77.5296   $77.53   $77.55   $77.50  
  Purchase #2 $232.37   12.762%   $262.0251   $262.03   $262.05   $262.00  
  Purchase #3 $175.78   3.488%   $181.9112   $181.91   $181.90   $181.90  
  Purchase #4 $160.76   11.772%   $179.6847   $179.68   $179.70   $179.70  
  Purchase #5 $119.44   10.664%   $132.1771   $132.18   $132.20   $132.20  
  Purchase #6 $58.53   9.434%   $64.0517   $64.05   $64.05   $64.10  
  Purchase #7 $249.98   9.679%   $274.1756   $274.18   $274.20   $274.20  
  7 purchase totals = $1,067.60       $1,171.5550   $1,171.56   $1,171.65   $1,171.60