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 $217.56   8.559%   $236.181   $236.18   $236.20   $236.20  
  Purchase #2 $96.75   3.720%   $100.3491   $100.35   $100.35   $100.30  
  Purchase #3 $71.49   7.247%   $76.6709   $76.67   $76.65   $76.70  
  Purchase #4 $54.83   5.606%   $57.9038   $57.90   $57.90   $57.90  
  Purchase #5 $118.42   9.460%   $129.6225   $129.62   $129.60   $129.60  
  Purchase #6 $79.90   9.600%   $87.5704   $87.57   $87.55   $87.60  
  Purchase #7 $105.70   9.219%   $115.4445   $115.44   $115.45   $115.40  
  7 purchase totals = $744.65       $803.7422   $803.73   $803.70   $803.70