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 $85.39   8.364%   $92.532   $92.53   $92.55   $92.50  
  Purchase #2 $170.84   10.446%   $188.6859   $188.69   $188.70   $188.70  
  Purchase #3 $216.33   7.490%   $232.5331   $232.53   $232.55   $232.50  
  Purchase #4 $147.58   7.262%   $158.2973   $158.30   $158.30   $158.30  
  Purchase #5 $133.88   5.509%   $141.2554   $141.26   $141.25   $141.30  
  Purchase #6 $242.65   6.596%   $258.6552   $258.66   $258.65   $258.70  
  Purchase #7 $161.41   6.322%   $171.6143   $171.61   $171.60   $171.60  
  7 purchase totals = $1,158.08       $1,243.5732   $1,243.58   $1,243.60   $1,243.60