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 $73.45   5.539%   $77.5184   $77.52   $77.50   $77.50  
  Purchase #2 $182.46   11.805%   $203.9994   $204.00   $204.00   $204.00  
  Purchase #3 $174.66   11.810%   $195.2873   $195.29   $195.30   $195.30  
  Purchase #4 $230.73   8.760%   $250.9419   $250.94   $250.95   $250.90  
  Purchase #5 $57.43   10.617%   $63.5273   $63.53   $63.55   $63.50  
  Purchase #6 $84.92   10.378%   $93.733   $93.73   $93.75   $93.70  
  Purchase #7 $186.61   3.261%   $192.6954   $192.70   $192.70   $192.70  
  7 purchase totals = $990.26       $1,077.7027   $1,077.71   $1,077.75   $1,077.60