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 $73.95   13.161%   $83.6826   $83.68   $83.70   $83.70  
  Purchase #2 $169.44   6.736%   $180.8535   $180.85   $180.85   $180.90  
  Purchase #3 $142.79   7.819%   $153.9548   $153.95   $153.95   $154.00  
  Purchase #4 $56.92   9.561%   $62.3621   $62.36   $62.35   $62.40  
  Purchase #5 $142.66   7.308%   $153.0856   $153.09   $153.10   $153.10  
  Purchase #6 $244.48   10.740%   $270.7372   $270.74   $270.75   $270.70  
  Purchase #7 $65.83   10.869%   $72.9851   $72.99   $73.00   $73.00  
  7 purchase totals = $896.07       $977.6609   $977.66   $977.70   $977.80