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 $246.33   8.607%   $267.5316   $267.53   $267.55   $267.50  
  Purchase #2 $219.77   6.338%   $233.699   $233.70   $233.70   $233.70  
  Purchase #3 $199.56   6.130%   $211.793   $211.79   $211.80   $211.80  
  Purchase #4 $241.89   9.678%   $265.3001   $265.30   $265.30   $265.30  
  Purchase #5 $162.84   3.820%   $169.0605   $169.06   $169.05   $169.10  
  Purchase #6 $107.72   4.277%   $112.3272   $112.33   $112.35   $112.30  
  Purchase #7 $164.62   11.411%   $183.4048   $183.40   $183.40   $183.40  
  7 purchase totals = $1,342.73       $1,443.1162   $1,443.11   $1,443.15   $1,443.10