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 $118.54   13.619%   $134.684   $134.68   $134.70   $134.70  
  Purchase #2 $65.94   10.431%   $72.8182   $72.82   $72.80   $72.80  
  Purchase #3 $175.55   11.184%   $195.1835   $195.18   $195.20   $195.20  
  Purchase #4 $167.38   3.851%   $173.8258   $173.83   $173.85   $173.80  
  Purchase #5 $172.58   13.616%   $196.0785   $196.08   $196.10   $196.10  
  Purchase #6 $234.63   7.148%   $251.4014   $251.40   $251.40   $251.40  
  Purchase #7 $192.30   12.404%   $216.1529   $216.15   $216.15   $216.20  
  7 purchase totals = $1,126.92       $1,240.1443   $1,240.14   $1,240.20   $1,240.20