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 $153.32   9.329%   $167.6232   $167.62   $167.60   $167.60  
  Purchase #2 $162.29   10.694%   $179.6453   $179.65   $179.65   $179.60  
  Purchase #3 $17.65   3.379%   $18.2464   $18.25   $18.25   $18.20  
  Purchase #4 $63.56   5.263%   $66.9052   $66.91   $66.90   $66.90  
  Purchase #5 $87.91   13.116%   $99.4403   $99.44   $99.45   $99.40  
  Purchase #6 $29.48   3.643%   $30.554   $30.55   $30.55   $30.60  
  Purchase #7 $235.50   3.438%   $243.5965   $243.60   $243.60   $243.60  
  7 purchase totals = $749.71       $806.0109   $806.02   $806.00   $805.90