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 $136.56   3.288%   $141.0501   $141.05   $141.05   $141.10  
  Purchase #2 $195.97   5.612%   $206.9678   $206.97   $206.95   $207.00  
  Purchase #3 $31.61   11.784%   $35.3349   $35.33   $35.35   $35.30  
  Purchase #4 $208.91   6.494%   $222.4766   $222.48   $222.50   $222.50  
  Purchase #5 $85.33   3.347%   $88.186   $88.19   $88.20   $88.20  
  Purchase #6 $55.57   11.380%   $61.8939   $61.89   $61.90   $61.90  
  Purchase #7 $197.74   7.561%   $212.6911   $212.69   $212.70   $212.70  
  7 purchase totals = $911.69       $968.6004   $968.60   $968.65   $968.70