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 $39.43   4.756%   $41.3053   $41.31   $41.30   $41.30  
  Purchase #2 $100.99   11.363%   $112.4655   $112.47   $112.45   $112.50  
  Purchase #3 $69.45   3.741%   $72.0481   $72.05   $72.05   $72.00  
  Purchase #4 $250.57   6.686%   $267.3231   $267.32   $267.30   $267.30  
  Purchase #5 $220.85   6.331%   $234.832   $234.83   $234.85   $234.80  
  Purchase #6 $13.53   10.211%   $14.9115   $14.91   $14.90   $14.90  
  Purchase #7 $160.35   4.183%   $167.0574   $167.06   $167.05   $167.10  
  7 purchase totals = $855.17       $909.9429   $909.95   $909.90   $909.90