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 $196.92   13.126%   $222.7677   $222.77   $222.75   $222.80  
  Purchase #2 $149.96   8.522%   $162.7396   $162.74   $162.75   $162.70  
  Purchase #3 $128.52   13.784%   $146.2352   $146.24   $146.25   $146.20  
  Purchase #4 $86.73   5.834%   $91.7898   $91.79   $91.80   $91.80  
  Purchase #5 $162.91   3.748%   $169.0159   $169.02   $169.00   $169.00  
  Purchase #6 $232.40   7.628%   $250.1275   $250.13   $250.15   $250.10  
  Purchase #7 $156.99   4.847%   $164.5993   $164.60   $164.60   $164.60  
  7 purchase totals = $1,114.43       $1,207.2750   $1,207.29   $1,207.30   $1,207.20