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 $79.93   13.356%   $90.6055   $90.61   $90.60   $90.60  
  Purchase #2 $51.58   9.200%   $56.3254   $56.33   $56.35   $56.30  
  Purchase #3 $226.28   12.541%   $254.6578   $254.66   $254.65   $254.70  
  Purchase #4 $147.61   12.733%   $166.4052   $166.41   $166.40   $166.40  
  Purchase #5 $156.70   13.805%   $178.3324   $178.33   $178.35   $178.30  
  Purchase #6 $250.37   13.379%   $283.867   $283.87   $283.85   $283.90  
  Purchase #7 $157.40   9.294%   $172.0288   $172.03   $172.05   $172.00  
  7 purchase totals = $1,069.87       $1,202.2221   $1,202.24   $1,202.25   $1,202.20