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 $207.39   5.277%   $218.334   $218.33   $218.35   $218.30  
  Purchase #2 $56.44   7.646%   $60.7554   $60.76   $60.75   $60.80  
  Purchase #3 $151.31   8.765%   $164.5723   $164.57   $164.55   $164.60  
  Purchase #4 $55.58   6.827%   $59.3744   $59.37   $59.35   $59.40  
  Purchase #5 $174.25   11.821%   $194.8481   $194.85   $194.85   $194.80  
  Purchase #6 $5.28   4.331%   $5.5087   $5.51   $5.50   $5.50  
  Purchase #7 $22.88   7.762%   $24.6559   $24.66   $24.65   $24.70  
  7 purchase totals = $673.13       $728.0488   $728.05   $728.00   $728.10