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 $157.53   6.483%   $167.7427   $167.74   $167.75   $167.70  
  Purchase #2 $54.41   12.613%   $61.2727   $61.27   $61.25   $61.30  
  Purchase #3 $154.40   6.239%   $164.033   $164.03   $164.05   $164.00  
  Purchase #4 $74.36   5.155%   $78.1933   $78.19   $78.20   $78.20  
  Purchase #5 $123.48   9.610%   $135.3464   $135.35   $135.35   $135.30  
  Purchase #6 $164.33   4.505%   $171.7331   $171.73   $171.75   $171.70  
  Purchase #7 $232.77   6.562%   $248.0444   $248.04   $248.05   $248.00  
  7 purchase totals = $961.28       $1,026.3656   $1,026.35   $1,026.40   $1,026.20