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 $239.86   11.503%   $267.4511   $267.45   $267.45   $267.50  
  Purchase #2 $36.90   3.516%   $38.1974   $38.20   $38.20   $38.20  
  Purchase #3 $167.25   5.534%   $176.5056   $176.51   $176.50   $176.50  
  Purchase #4 $114.30   6.435%   $121.6552   $121.66   $121.65   $121.70  
  Purchase #5 $198.50   5.773%   $209.9594   $209.96   $209.95   $210.00  
  Purchase #6 $214.40   13.667%   $243.702   $243.70   $243.70   $243.70  
  Purchase #7 $164.60   12.132%   $184.5693   $184.57   $184.55   $184.60  
  7 purchase totals = $1,135.81       $1,242.0400   $1,242.05   $1,242.00   $1,242.20