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 $7.91   12.361%   $8.8878   $8.89   $8.90   $8.90  
  Purchase #2 $194.61   9.640%   $213.3704   $213.37   $213.35   $213.40  
  Purchase #3 $223.78   13.463%   $253.9075   $253.91   $253.90   $253.90  
  Purchase #4 $89.50   10.412%   $98.8187   $98.82   $98.80   $98.80  
  Purchase #5 $19.88   12.770%   $22.4187   $22.42   $22.40   $22.40  
  Purchase #6 $9.50   8.620%   $10.3189   $10.32   $10.30   $10.30  
  Purchase #7 $86.99   10.347%   $95.9909   $95.99   $96.00   $96.00  
  7 purchase totals = $632.17       $703.7129   $703.72   $703.65   $703.70