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 $11.65   5.210%   $12.257   $12.26   $12.25   $12.30  
  Purchase #2 $54.63   12.588%   $61.5068   $61.51   $61.50   $61.50  
  Purchase #3 $161.81   3.177%   $166.9507   $166.95   $166.95   $167.00  
  Purchase #4 $134.42   5.372%   $141.641   $141.64   $141.65   $141.60  
  Purchase #5 $14.98   7.133%   $16.0485   $16.05   $16.05   $16.00  
  Purchase #6 $202.78   11.498%   $226.0956   $226.10   $226.10   $226.10  
  Purchase #7 $217.63   4.136%   $226.6312   $226.63   $226.65   $226.60  
  7 purchase totals = $797.90       $851.1308   $851.14   $851.15   $851.10