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 $61.26   4.229%   $63.8507   $63.85   $63.85   $63.90  
  Purchase #2 $114.84   5.734%   $121.4249   $121.42   $121.40   $121.40  
  Purchase #3 $171.98   12.771%   $193.9436   $193.94   $193.95   $193.90  
  Purchase #4 $90.71   11.210%   $100.8786   $100.88   $100.90   $100.90  
  Purchase #5 $8.87   6.267%   $9.4259   $9.43   $9.45   $9.40  
  Purchase #6 $204.29   13.458%   $231.7833   $231.78   $231.80   $231.80  
  Purchase #7 $25.59   9.484%   $28.017   $28.02   $28.00   $28.00  
  7 purchase totals = $677.54       $749.3240   $749.32   $749.35   $749.30