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 $59.65   12.835%   $67.3061   $67.31   $67.30   $67.30  
  Purchase #2 $148.60   4.662%   $155.5277   $155.53   $155.55   $155.50  
  Purchase #3 $211.29   13.529%   $239.8754   $239.88   $239.90   $239.90  
  Purchase #4 $101.81   7.347%   $109.29   $109.29   $109.30   $109.30  
  Purchase #5 $235.87   13.376%   $267.42   $267.42   $267.40   $267.40  
  Purchase #6 $110.47   9.287%   $120.7293   $120.73   $120.75   $120.70  
  Purchase #7 $11.72   4.711%   $12.2721   $12.27   $12.25   $12.30  
  7 purchase totals = $879.41       $972.4206   $972.43   $972.45   $972.40