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 $109.86   8.118%   $118.7784   $118.78   $118.80   $118.80  
  Purchase #2 $177.78   3.446%   $183.9063   $183.91   $183.90   $183.90  
  Purchase #3 $32.47   6.626%   $34.6215   $34.62   $34.60   $34.60  
  Purchase #4 $216.41   7.331%   $232.275   $232.28   $232.30   $232.30  
  Purchase #5 $33.76   6.225%   $35.8616   $35.86   $35.85   $35.90  
  Purchase #6 $125.47   11.693%   $140.1412   $140.14   $140.15   $140.10  
  Purchase #7 $246.68   8.368%   $267.3222   $267.32   $267.30   $267.30  
  7 purchase totals = $942.43       $1,012.9062   $1,012.91   $1,012.90   $1,012.90