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 $228.97   13.533%   $259.9565   $259.96   $259.95   $260.00  
  Purchase #2 $46.57   8.322%   $50.4456   $50.45   $50.45   $50.40  
  Purchase #3 $5.33   12.671%   $6.0054   $6.01   $6.00   $6.00  
  Purchase #4 $126.72   10.349%   $139.8343   $139.83   $139.85   $139.80  
  Purchase #5 $77.32   12.772%   $87.1953   $87.20   $87.20   $87.20  
  Purchase #6 $170.77   8.763%   $185.7346   $185.73   $185.75   $185.70  
  Purchase #7 $171.54   8.601%   $186.2942   $186.29   $186.30   $186.30  
  7 purchase totals = $827.22       $915.4659   $915.47   $915.50   $915.40