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 $91.25   3.677%   $94.6053   $94.61   $94.60   $94.60  
  Purchase #2 $84.56   6.151%   $89.7613   $89.76   $89.75   $89.80  
  Purchase #3 $193.44   10.680%   $214.0994   $214.10   $214.10   $214.10  
  Purchase #4 $202.34   12.336%   $227.3007   $227.30   $227.30   $227.30  
  Purchase #5 $113.71   4.285%   $118.5825   $118.58   $118.60   $118.60  
  Purchase #6 $128.70   4.237%   $134.153   $134.15   $134.15   $134.20  
  Purchase #7 $200.94   6.801%   $214.6059   $214.61   $214.60   $214.60  
  7 purchase totals = $1,014.94       $1,093.1081   $1,093.11   $1,093.10   $1,093.20