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 $211.49   11.715%   $236.2661   $236.27   $236.25   $236.30  
  Purchase #2 $152.28   10.298%   $167.9618   $167.96   $167.95   $168.00  
  Purchase #3 $80.99   3.259%   $83.6295   $83.63   $83.65   $83.60  
  Purchase #4 $201.33   3.290%   $207.9538   $207.95   $207.95   $208.00  
  Purchase #5 $222.48   4.570%   $232.6473   $232.65   $232.65   $232.60  
  Purchase #6 $219.91   12.140%   $246.6071   $246.61   $246.60   $246.60  
  Purchase #7 $132.93   12.294%   $149.2724   $149.27   $149.25   $149.30  
  7 purchase totals = $1,221.41       $1,324.3380   $1,324.34   $1,324.30   $1,324.40