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 $66.31   3.866%   $68.8735   $68.87   $68.85   $68.90  
  Purchase #2 $169.85   8.314%   $183.9713   $183.97   $183.95   $184.00  
  Purchase #3 $247.88   9.144%   $270.5461   $270.55   $270.55   $270.50  
  Purchase #4 $166.66   11.592%   $185.9792   $185.98   $186.00   $186.00  
  Purchase #5 $15.71   5.323%   $16.5462   $16.55   $16.55   $16.50  
  Purchase #6 $33.56   5.483%   $35.4001   $35.40   $35.40   $35.40  
  Purchase #7 $32.27   10.212%   $35.5654   $35.57   $35.55   $35.60  
  7 purchase totals = $732.24       $796.8818   $796.89   $796.85   $796.90