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 $234.58   10.516%   $259.2484   $259.25   $259.25   $259.20  
  Purchase #2 $213.43   13.539%   $242.3263   $242.33   $242.35   $242.30  
  Purchase #3 $203.68   5.240%   $214.3528   $214.35   $214.35   $214.40  
  Purchase #4 $154.96   8.831%   $168.6445   $168.64   $168.65   $168.60  
  Purchase #5 $60.79   5.780%   $64.3037   $64.30   $64.30   $64.30  
  Purchase #6 $202.91   11.331%   $225.9017   $225.90   $225.90   $225.90  
  Purchase #7 $156.61   10.591%   $173.1966   $173.20   $173.20   $173.20  
  7 purchase totals = $1,226.96       $1,347.9740   $1,347.97   $1,348.00   $1,347.90