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 $69.41   9.760%   $76.1844   $76.18   $76.20   $76.20  
  Purchase #2 $227.97   8.587%   $247.5458   $247.55   $247.55   $247.50  
  Purchase #3 $87.90   7.824%   $94.7773   $94.78   $94.80   $94.80  
  Purchase #4 $48.59   9.301%   $53.1094   $53.11   $53.10   $53.10  
  Purchase #5 $20.87   13.659%   $23.7206   $23.72   $23.70   $23.70  
  Purchase #6 $237.73   8.196%   $257.2144   $257.21   $257.20   $257.20  
  Purchase #7 $164.51   10.421%   $181.6536   $181.65   $181.65   $181.70  
  7 purchase totals = $856.98       $934.2055   $934.20   $934.20   $934.20