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 $114.54   13.134%   $129.5837   $129.58   $129.60   $129.60  
  Purchase #2 $196.66   7.763%   $211.9267   $211.93   $211.95   $211.90  
  Purchase #3 $192.66   4.838%   $201.9809   $201.98   $202.00   $202.00  
  Purchase #4 $192.45   5.704%   $203.4273   $203.43   $203.45   $203.40  
  Purchase #5 $195.41   11.144%   $217.1865   $217.19   $217.20   $217.20  
  Purchase #6 $143.46   6.362%   $152.5869   $152.59   $152.60   $152.60  
  Purchase #7 $97.51   3.674%   $101.0925   $101.09   $101.10   $101.10  
  7 purchase totals = $1,132.69       $1,217.7845   $1,217.79   $1,217.90   $1,217.80