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 $111.39   7.540%   $119.7888   $119.79   $119.80   $119.80  
  Purchase #2 $166.89   5.549%   $176.1507   $176.15   $176.15   $176.20  
  Purchase #3 $56.77   3.874%   $58.9693   $58.97   $58.95   $59.00  
  Purchase #4 $143.94   6.313%   $153.0269   $153.03   $153.05   $153.00  
  Purchase #5 $233.37   8.526%   $253.2671   $253.27   $253.25   $253.30  
  Purchase #6 $154.98   6.398%   $164.8956   $164.90   $164.90   $164.90  
  Purchase #7 $108.39   11.128%   $120.4516   $120.45   $120.45   $120.50  
  7 purchase totals = $975.73       $1,046.5500   $1,046.56   $1,046.55   $1,046.70