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 $48.73   8.731%   $52.9846   $52.98   $53.00   $53.00  
  Purchase #2 $243.38   7.861%   $262.5121   $262.51   $262.50   $262.50  
  Purchase #3 $146.33   6.723%   $156.1678   $156.17   $156.15   $156.20  
  Purchase #4 $25.53   8.189%   $27.6207   $27.62   $27.60   $27.60  
  Purchase #5 $139.77   3.452%   $144.5949   $144.59   $144.60   $144.60  
  Purchase #6 $228.60   10.568%   $252.7584   $252.76   $252.75   $252.80  
  Purchase #7 $117.66   3.731%   $122.0499   $122.05   $122.05   $122.00  
  7 purchase totals = $950.00       $1,018.6884   $1,018.68   $1,018.65   $1,018.70