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 $79.49   10.657%   $87.9612   $87.96   $87.95   $88.00  
  Purchase #2 $119.64   10.375%   $132.0527   $132.05   $132.05   $132.10  
  Purchase #3 $129.67   13.360%   $146.9939   $146.99   $147.00   $147.00  
  Purchase #4 $167.96   6.508%   $178.8908   $178.89   $178.90   $178.90  
  Purchase #5 $125.26   4.128%   $130.4307   $130.43   $130.45   $130.40  
  Purchase #6 $41.46   6.143%   $44.0069   $44.01   $44.00   $44.00  
  Purchase #7 $198.30   3.145%   $204.5365   $204.54   $204.55   $204.50  
  7 purchase totals = $861.78       $924.8727   $924.87   $924.90   $924.90