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 $52.34   10.466%   $57.8179   $57.82   $57.80   $57.80  
  Purchase #2 $234.29   10.511%   $258.9162   $258.92   $258.90   $258.90  
  Purchase #3 $165.74   4.658%   $173.4602   $173.46   $173.45   $173.50  
  Purchase #4 $14.49   6.144%   $15.3803   $15.38   $15.40   $15.40  
  Purchase #5 $95.49   6.851%   $102.032   $102.03   $102.05   $102.00  
  Purchase #6 $126.92   13.226%   $143.7064   $143.71   $143.70   $143.70  
  Purchase #7 $41.85   4.490%   $43.7291   $43.73   $43.75   $43.70  
  7 purchase totals = $731.12       $795.0421   $795.05   $795.05   $795.00