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 $34.76   11.797%   $38.8606   $38.86   $38.85   $38.90  
  Purchase #2 $107.71   13.309%   $122.0451   $122.05   $122.05   $122.00  
  Purchase #3 $211.86   4.685%   $221.7856   $221.79   $221.80   $221.80  
  Purchase #4 $234.95   8.639%   $255.2473   $255.25   $255.25   $255.20  
  Purchase #5 $62.46   11.487%   $69.6348   $69.63   $69.65   $69.60  
  Purchase #6 $174.75   11.343%   $194.5719   $194.57   $194.55   $194.60  
  Purchase #7 $228.88   11.320%   $254.7892   $254.79   $254.80   $254.80  
  7 purchase totals = $1,055.37       $1,156.9345   $1,156.94   $1,156.95   $1,156.90