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 $195.83   11.705%   $218.7519   $218.75   $218.75   $218.80  
  Purchase #2 $240.80   10.443%   $265.9467   $265.95   $265.95   $265.90  
  Purchase #3 $88.79   4.409%   $92.7048   $92.70   $92.70   $92.70  
  Purchase #4 $158.67   5.274%   $167.0383   $167.04   $167.05   $167.00  
  Purchase #5 $61.29   8.623%   $66.575   $66.58   $66.60   $66.60  
  Purchase #6 $9.48   6.102%   $10.0585   $10.06   $10.05   $10.10  
  Purchase #7 $184.45   5.321%   $194.2646   $194.26   $194.25   $194.30  
  7 purchase totals = $939.31       $1,015.3398   $1,015.34   $1,015.35   $1,015.40