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 $84.68   10.193%   $93.3114   $93.31   $93.30   $93.30  
  Purchase #2 $203.64   11.791%   $227.6512   $227.65   $227.65   $227.70  
  Purchase #3 $196.66   7.729%   $211.8599   $211.86   $211.85   $211.90  
  Purchase #4 $146.47   5.535%   $154.5771   $154.58   $154.60   $154.60  
  Purchase #5 $134.65   6.711%   $143.6864   $143.69   $143.70   $143.70  
  Purchase #6 $202.75   3.696%   $210.2436   $210.24   $210.25   $210.20  
  Purchase #7 $128.88   9.245%   $140.795   $140.80   $140.80   $140.80  
  7 purchase totals = $1,097.73       $1,182.1246   $1,182.13   $1,182.15   $1,182.20