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 $88.87   9.162%   $97.0123   $97.01   $97.00   $97.00  
  Purchase #2 $119.63   9.173%   $130.6037   $130.60   $130.60   $130.60  
  Purchase #3 $109.35   9.488%   $119.7251   $119.73   $119.75   $119.70  
  Purchase #4 $100.83   4.626%   $105.4944   $105.49   $105.50   $105.50  
  Purchase #5 $57.50   6.598%   $61.2939   $61.29   $61.30   $61.30  
  Purchase #6 $206.61   6.585%   $220.2153   $220.22   $220.20   $220.20  
  Purchase #7 $28.56   4.687%   $29.8986   $29.90   $29.90   $29.90  
  7 purchase totals = $711.35       $764.2433   $764.24   $764.25   $764.20