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 $229.69   6.564%   $244.7669   $244.77   $244.75   $244.80  
  Purchase #2 $105.74   13.394%   $119.9028   $119.90   $119.90   $119.90  
  Purchase #3 $51.83   3.429%   $53.6073   $53.61   $53.60   $53.60  
  Purchase #4 $235.40   4.349%   $245.6375   $245.64   $245.65   $245.60  
  Purchase #5 $156.94   7.745%   $169.095   $169.10   $169.10   $169.10  
  Purchase #6 $63.46   3.561%   $65.7198   $65.72   $65.70   $65.70  
  Purchase #7 $105.56   3.426%   $109.1765   $109.18   $109.20   $109.20  
  7 purchase totals = $948.62       $1,007.9058   $1,007.92   $1,007.90   $1,007.90