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 $85.41   11.268%   $95.034   $95.03   $95.05   $95.00  
  Purchase #2 $57.55   5.649%   $60.801   $60.80   $60.80   $60.80  
  Purchase #3 $133.58   12.823%   $150.709   $150.71   $150.70   $150.70  
  Purchase #4 $206.79   4.418%   $215.926   $215.93   $215.95   $215.90  
  Purchase #5 $96.34   7.276%   $103.3497   $103.35   $103.35   $103.30  
  Purchase #6 $8.98   5.781%   $9.4991   $9.50   $9.50   $9.50  
  Purchase #7 $13.40   8.608%   $14.5535   $14.55   $14.55   $14.60  
  7 purchase totals = $602.05       $649.8723   $649.87   $649.90   $649.80