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 $210.88   13.230%   $238.7794   $238.78   $238.80   $238.80  
  Purchase #2 $160.27   8.338%   $173.6333   $173.63   $173.65   $173.60  
  Purchase #3 $51.30   12.440%   $57.6817   $57.68   $57.70   $57.70  
  Purchase #4 $221.54   11.638%   $247.3228   $247.32   $247.30   $247.30  
  Purchase #5 $144.40   8.440%   $156.5874   $156.59   $156.60   $156.60  
  Purchase #6 $92.76   3.535%   $96.0391   $96.04   $96.05   $96.00  
  Purchase #7 $53.46   12.836%   $60.3221   $60.32   $60.30   $60.30  
  7 purchase totals = $934.61       $1,030.3658   $1,030.36   $1,030.40   $1,030.30