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 $241.86   6.818%   $258.35   $258.35   $258.35   $258.40  
  Purchase #2 $152.91   3.197%   $157.7985   $157.80   $157.80   $157.80  
  Purchase #3 $155.89   5.302%   $164.1553   $164.16   $164.15   $164.20  
  Purchase #4 $104.80   6.624%   $111.742   $111.74   $111.75   $111.70  
  Purchase #5 $181.67   12.104%   $203.6593   $203.66   $203.65   $203.70  
  Purchase #6 $157.73   7.334%   $169.2979   $169.30   $169.30   $169.30  
  Purchase #7 $114.37   13.369%   $129.6601   $129.66   $129.65   $129.70  
  7 purchase totals = $1,109.23       $1,194.6631   $1,194.67   $1,194.65   $1,194.80