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 $118.74   11.121%   $131.9451   $131.95   $131.95   $131.90  
  Purchase #2 $233.82   10.191%   $257.6486   $257.65   $257.65   $257.60  
  Purchase #3 $114.85   10.637%   $127.0666   $127.07   $127.05   $127.10  
  Purchase #4 $145.31   7.628%   $156.3942   $156.39   $156.40   $156.40  
  Purchase #5 $171.41   12.724%   $193.2202   $193.22   $193.20   $193.20  
  Purchase #6 $202.45   4.438%   $211.4347   $211.43   $211.45   $211.40  
  Purchase #7 $99.38   7.388%   $106.7222   $106.72   $106.70   $106.70  
  7 purchase totals = $1,085.96       $1,184.4316   $1,184.43   $1,184.40   $1,184.30