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 $212.60   12.745%   $239.6959   $239.70   $239.70   $239.70  
  Purchase #2 $125.33   11.154%   $139.3093   $139.31   $139.30   $139.30  
  Purchase #3 $130.27   10.181%   $143.5328   $143.53   $143.55   $143.50  
  Purchase #4 $51.82   4.162%   $53.9767   $53.98   $54.00   $54.00  
  Purchase #5 $58.64   11.639%   $65.4651   $65.47   $65.45   $65.50  
  Purchase #6 $177.65   11.873%   $198.7424   $198.74   $198.75   $198.70  
  Purchase #7 $185.70   4.604%   $194.2496   $194.25   $194.25   $194.20  
  7 purchase totals = $942.01       $1,034.9718   $1,034.98   $1,035.00   $1,034.90