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 $63.55   4.328%   $66.3004   $66.30   $66.30   $66.30  
  Purchase #2 $142.26   3.263%   $146.9019   $146.90   $146.90   $146.90  
  Purchase #3 $169.61   10.732%   $187.8125   $187.81   $187.80   $187.80  
  Purchase #4 $66.56   3.223%   $68.7052   $68.71   $68.70   $68.70  
  Purchase #5 $203.65   3.703%   $211.1912   $211.19   $211.20   $211.20  
  Purchase #6 $170.56   7.414%   $183.2053   $183.21   $183.20   $183.20  
  Purchase #7 $161.47   4.395%   $168.5666   $168.57   $168.55   $168.60  
  7 purchase totals = $977.66       $1,032.6831   $1,032.69   $1,032.65   $1,032.70