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 $227.34   4.454%   $237.4657   $237.47   $237.45   $237.50  
  Purchase #2 $233.45   6.247%   $248.0336   $248.03   $248.05   $248.00  
  Purchase #3 $228.84   13.364%   $259.4222   $259.42   $259.40   $259.40  
  Purchase #4 $149.35   13.610%   $169.6765   $169.68   $169.70   $169.70  
  Purchase #5 $203.30   3.779%   $210.9827   $210.98   $211.00   $211.00  
  Purchase #6 $6.37   11.697%   $7.1151   $7.12   $7.10   $7.10  
  Purchase #7 $168.30   11.481%   $187.6225   $187.62   $187.60   $187.60  
  7 purchase totals = $1,216.95       $1,320.3183   $1,320.32   $1,320.30   $1,320.30