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 $91.68   4.689%   $95.9789   $95.98   $96.00   $96.00  
  Purchase #2 $54.54   12.771%   $61.5053   $61.51   $61.50   $61.50  
  Purchase #3 $128.60   6.856%   $137.4168   $137.42   $137.40   $137.40  
  Purchase #4 $109.25   4.635%   $114.3137   $114.31   $114.30   $114.30  
  Purchase #5 $156.33   5.697%   $165.2361   $165.24   $165.25   $165.20  
  Purchase #6 $209.55   13.418%   $237.6674   $237.67   $237.65   $237.70  
  Purchase #7 $185.99   12.665%   $209.5456   $209.55   $209.55   $209.50  
  7 purchase totals = $935.94       $1,021.6638   $1,021.68   $1,021.65   $1,021.60