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 $114.54   7.634%   $123.284   $123.28   $123.30   $123.30  
  Purchase #2 $95.37   6.624%   $101.6873   $101.69   $101.70   $101.70  
  Purchase #3 $79.79   7.140%   $85.487   $85.49   $85.50   $85.50  
  Purchase #4 $182.87   9.130%   $199.566   $199.57   $199.55   $199.60  
  Purchase #5 $22.35   8.815%   $24.3202   $24.32   $24.30   $24.30  
  Purchase #6 $90.76   3.860%   $94.2633   $94.26   $94.25   $94.30  
  Purchase #7 $163.67   12.620%   $184.3252   $184.33   $184.35   $184.30  
  7 purchase totals = $749.35       $812.9330   $812.94   $812.95   $813.00