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 $68.91   12.583%   $77.5809   $77.58   $77.60   $77.60  
  Purchase #2 $118.93   8.547%   $129.0949   $129.09   $129.10   $129.10  
  Purchase #3 $183.58   6.563%   $195.6284   $195.63   $195.65   $195.60  
  Purchase #4 $191.64   11.585%   $213.8415   $213.84   $213.85   $213.80  
  Purchase #5 $243.41   4.429%   $254.1906   $254.19   $254.20   $254.20  
  Purchase #6 $193.33   13.796%   $220.0018   $220.00   $220.00   $220.00  
  Purchase #7 $242.67   5.201%   $255.2913   $255.29   $255.30   $255.30  
  7 purchase totals = $1,242.47       $1,345.6294   $1,345.62   $1,345.70   $1,345.60