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 $222.91   13.395%   $252.7688   $252.77   $252.75   $252.80  
  Purchase #2 $185.78   9.293%   $203.0445   $203.04   $203.05   $203.00  
  Purchase #3 $28.67   3.186%   $29.5834   $29.58   $29.60   $29.60  
  Purchase #4 $221.56   5.572%   $233.9053   $233.91   $233.90   $233.90  
  Purchase #5 $89.88   6.216%   $95.4669   $95.47   $95.45   $95.50  
  Purchase #6 $247.63   3.554%   $256.4308   $256.43   $256.45   $256.40  
  Purchase #7 $78.94   7.386%   $84.7705   $84.77   $84.75   $84.80  
  7 purchase totals = $1,075.37       $1,155.9702   $1,155.97   $1,155.95   $1,156.00