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 $92.41   11.411%   $102.9549   $102.95   $102.95   $103.00  
  Purchase #2 $188.48   11.161%   $209.5163   $209.52   $209.50   $209.50  
  Purchase #3 $55.61   10.106%   $61.2299   $61.23   $61.25   $61.20  
  Purchase #4 $138.61   5.525%   $146.2682   $146.27   $146.25   $146.30  
  Purchase #5 $16.58   5.714%   $17.5274   $17.53   $17.55   $17.50  
  Purchase #6 $243.85   9.597%   $267.2523   $267.25   $267.25   $267.30  
  Purchase #7 $226.99   8.347%   $245.9369   $245.94   $245.95   $245.90  
  7 purchase totals = $962.53       $1,050.6859   $1,050.69   $1,050.70   $1,050.70