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 $152.79   10.631%   $169.0331   $169.03   $169.05   $169.00  
  Purchase #2 $225.49   4.451%   $235.5266   $235.53   $235.55   $235.50  
  Purchase #3 $92.76   13.476%   $105.2603   $105.26   $105.25   $105.30  
  Purchase #4 $99.61   4.273%   $103.8663   $103.87   $103.85   $103.90  
  Purchase #5 $220.87   8.414%   $239.454   $239.45   $239.45   $239.50  
  Purchase #6 $241.98   5.265%   $254.7202   $254.72   $254.70   $254.70  
  Purchase #7 $241.40   5.618%   $254.9619   $254.96   $254.95   $255.00  
  7 purchase totals = $1,274.90       $1,362.8224   $1,362.82   $1,362.80   $1,362.90