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 $63.36   11.615%   $70.7193   $70.72   $70.70   $70.70  
  Purchase #2 $194.81   12.636%   $219.4262   $219.43   $219.45   $219.40  
  Purchase #3 $151.98   8.836%   $165.409   $165.41   $165.40   $165.40  
  Purchase #4 $51.82   8.821%   $56.391   $56.39   $56.40   $56.40  
  Purchase #5 $211.96   3.650%   $219.6965   $219.70   $219.70   $219.70  
  Purchase #6 $217.27   12.509%   $244.4483   $244.45   $244.45   $244.40  
  Purchase #7 $12.40   11.855%   $13.87   $13.87   $13.85   $13.90  
  7 purchase totals = $903.60       $989.9603   $989.97   $989.95   $989.90