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 $7.46   7.402%   $8.0122   $8.01   $8.00   $8.00  
  Purchase #2 $174.39   4.308%   $181.9027   $181.90   $181.90   $181.90  
  Purchase #3 $167.64   9.242%   $183.1333   $183.13   $183.15   $183.10  
  Purchase #4 $159.34   6.296%   $169.372   $169.37   $169.35   $169.40  
  Purchase #5 $150.68   3.612%   $156.1226   $156.12   $156.10   $156.10  
  Purchase #6 $96.76   3.117%   $99.776   $99.78   $99.80   $99.80  
  Purchase #7 $198.32   8.425%   $215.0285   $215.03   $215.05   $215.00  
  7 purchase totals = $954.59       $1,013.3473   $1,013.34   $1,013.35   $1,013.30