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 $236.94   13.788%   $269.6093   $269.61   $269.60   $269.60  
  Purchase #2 $54.74   3.491%   $56.651   $56.65   $56.65   $56.70  
  Purchase #3 $103.67   13.532%   $117.6986   $117.70   $117.70   $117.70  
  Purchase #4 $55.66   10.761%   $61.6496   $61.65   $61.65   $61.60  
  Purchase #5 $61.92   3.703%   $64.2129   $64.21   $64.20   $64.20  
  Purchase #6 $138.62   3.156%   $142.9948   $142.99   $143.00   $143.00  
  Purchase #7 $213.84   6.780%   $228.3384   $228.34   $228.35   $228.30  
  7 purchase totals = $865.39       $941.1546   $941.15   $941.15   $941.10