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 $125.88   6.167%   $133.643   $133.64   $133.65   $133.60  
  Purchase #2 $224.36   5.722%   $237.1979   $237.20   $237.20   $237.20  
  Purchase #3 $137.67   13.755%   $156.6065   $156.61   $156.60   $156.60  
  Purchase #4 $192.79   4.794%   $202.0324   $202.03   $202.05   $202.00  
  Purchase #5 $63.65   6.773%   $67.961   $67.96   $67.95   $68.00  
  Purchase #6 $81.82   4.803%   $85.7498   $85.75   $85.75   $85.70  
  Purchase #7 $161.82   4.431%   $168.9902   $168.99   $169.00   $169.00  
  7 purchase totals = $987.99       $1,052.1808   $1,052.18   $1,052.20   $1,052.10