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 $65.94   4.333%   $68.7972   $68.80   $68.80   $68.80  
  Purchase #2 $204.95   3.321%   $211.7564   $211.76   $211.75   $211.80  
  Purchase #3 $84.37   13.650%   $95.8865   $95.89   $95.90   $95.90  
  Purchase #4 $26.42   3.174%   $27.2586   $27.26   $27.25   $27.30  
  Purchase #5 $34.54   10.828%   $38.28   $38.28   $38.30   $38.30  
  Purchase #6 $13.49   12.782%   $15.2143   $15.21   $15.20   $15.20  
  Purchase #7 $231.61   4.790%   $242.7041   $242.70   $242.70   $242.70  
  7 purchase totals = $661.32       $699.8971   $699.90   $699.90   $700.00