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 $82.39   9.651%   $90.3415   $90.34   $90.35   $90.30  
  Purchase #2 $169.55   8.608%   $184.1449   $184.14   $184.15   $184.10  
  Purchase #3 $113.55   12.420%   $127.6529   $127.65   $127.65   $127.70  
  Purchase #4 $169.38   4.595%   $177.163   $177.16   $177.15   $177.20  
  Purchase #5 $67.71   5.584%   $71.4909   $71.49   $71.50   $71.50  
  Purchase #6 $205.40   5.253%   $216.1897   $216.19   $216.20   $216.20  
  Purchase #7 $134.60   9.426%   $147.2874   $147.29   $147.30   $147.30  
  7 purchase totals = $942.58       $1,014.2703   $1,014.26   $1,014.30   $1,014.30