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 $174.72   11.727%   $195.2094   $195.21   $195.20   $195.20  
  Purchase #2 $75.77   12.185%   $85.0026   $85.00   $85.00   $85.00  
  Purchase #3 $109.93   5.152%   $115.5936   $115.59   $115.60   $115.60  
  Purchase #4 $206.96   12.175%   $232.1574   $232.16   $232.15   $232.20  
  Purchase #5 $125.62   12.703%   $141.5775   $141.58   $141.60   $141.60  
  Purchase #6 $64.83   7.224%   $69.5133   $69.51   $69.50   $69.50  
  Purchase #7 $23.69   13.279%   $26.8358   $26.84   $26.85   $26.80  
  7 purchase totals = $781.52       $865.8896   $865.89   $865.90   $865.90