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 $239.55   11.869%   $267.9822   $267.98   $268.00   $268.00  
  Purchase #2 $184.27   8.109%   $199.2125   $199.21   $199.20   $199.20  
  Purchase #3 $225.86   13.171%   $255.608   $255.61   $255.60   $255.60  
  Purchase #4 $202.28   4.566%   $211.5161   $211.52   $211.50   $211.50  
  Purchase #5 $189.88   5.660%   $200.6272   $200.63   $200.65   $200.60  
  Purchase #6 $70.98   8.307%   $76.8763   $76.88   $76.90   $76.90  
  Purchase #7 $145.72   10.500%   $161.0206   $161.02   $161.00   $161.00  
  7 purchase totals = $1,258.54       $1,372.8429   $1,372.85   $1,372.85   $1,372.80