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 $58.32   4.585%   $60.994   $60.99   $61.00   $61.00  
  Purchase #2 $7.43   7.715%   $8.0032   $8.00   $8.00   $8.00  
  Purchase #3 $176.29   11.397%   $196.3818   $196.38   $196.40   $196.40  
  Purchase #4 $205.57   13.471%   $233.2623   $233.26   $233.25   $233.30  
  Purchase #5 $246.67   5.219%   $259.5437   $259.54   $259.55   $259.50  
  Purchase #6 $41.27   12.369%   $46.3747   $46.37   $46.35   $46.40  
  Purchase #7 $45.48   5.228%   $47.8577   $47.86   $47.85   $47.90  
  7 purchase totals = $781.03       $852.4174   $852.40   $852.40   $852.50