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 $61.29   12.207%   $68.7717   $68.77   $68.75   $68.80  
  Purchase #2 $183.37   10.681%   $202.9557   $202.96   $202.95   $203.00  
  Purchase #3 $76.91   13.431%   $87.2398   $87.24   $87.25   $87.20  
  Purchase #4 $31.64   10.295%   $34.8973   $34.90   $34.90   $34.90  
  Purchase #5 $223.90   7.862%   $241.503   $241.50   $241.50   $241.50  
  Purchase #6 $105.26   7.726%   $113.3924   $113.39   $113.40   $113.40  
  Purchase #7 $56.90   5.756%   $60.1752   $60.18   $60.20   $60.20  
  7 purchase totals = $739.27       $808.9351   $808.94   $808.95   $809.00