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 $188.25   3.862%   $195.5202   $195.52   $195.50   $195.50  
  Purchase #2 $122.99   6.358%   $130.8097   $130.81   $130.80   $130.80  
  Purchase #3 $151.94   5.822%   $160.7859   $160.79   $160.80   $160.80  
  Purchase #4 $199.43   7.435%   $214.2576   $214.26   $214.25   $214.30  
  Purchase #5 $183.87   3.298%   $189.934   $189.93   $189.95   $189.90  
  Purchase #6 $240.26   9.808%   $263.8247   $263.82   $263.80   $263.80  
  Purchase #7 $179.57   6.384%   $191.0337   $191.03   $191.05   $191.00  
  7 purchase totals = $1,266.31       $1,346.1658   $1,346.16   $1,346.15   $1,346.10