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 $219.25   10.787%   $242.9005   $242.90   $242.90   $242.90  
  Purchase #2 $186.42   3.716%   $193.3474   $193.35   $193.35   $193.30  
  Purchase #3 $31.33   8.735%   $34.0667   $34.07   $34.05   $34.10  
  Purchase #4 $145.28   8.463%   $157.575   $157.58   $157.60   $157.60  
  Purchase #5 $73.84   7.159%   $79.1262   $79.13   $79.15   $79.10  
  Purchase #6 $204.89   12.531%   $230.5648   $230.56   $230.55   $230.60  
  Purchase #7 $112.31   10.248%   $123.8195   $123.82   $123.80   $123.80  
  7 purchase totals = $973.32       $1,061.4001   $1,061.41   $1,061.40   $1,061.40