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 $189.97   10.526%   $209.9662   $209.97   $209.95   $210.00  
  Purchase #2 $244.74   11.369%   $272.5645   $272.56   $272.55   $272.60  
  Purchase #3 $67.57   10.608%   $74.7378   $74.74   $74.75   $74.70  
  Purchase #4 $72.94   6.631%   $77.7767   $77.78   $77.80   $77.80  
  Purchase #5 $148.66   7.412%   $159.6787   $159.68   $159.70   $159.70  
  Purchase #6 $69.93   12.329%   $78.5517   $78.55   $78.55   $78.60  
  Purchase #7 $167.81   12.414%   $188.6419   $188.64   $188.65   $188.60  
  7 purchase totals = $961.62       $1,061.9175   $1,061.92   $1,061.95   $1,062.00