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 $176.87   12.309%   $198.6409   $198.64   $198.65   $198.60  
  Purchase #2 $222.89   8.725%   $242.3372   $242.34   $242.35   $242.30  
  Purchase #3 $235.96   11.522%   $263.1473   $263.15   $263.15   $263.10  
  Purchase #4 $66.93   4.303%   $69.81   $69.81   $69.80   $69.80  
  Purchase #5 $173.69   12.439%   $195.2953   $195.30   $195.30   $195.30  
  Purchase #6 $84.78   3.233%   $87.5209   $87.52   $87.50   $87.50  
  Purchase #7 $192.40   6.369%   $204.654   $204.65   $204.65   $204.70  
  7 purchase totals = $1,153.52       $1,261.4056   $1,261.41   $1,261.40   $1,261.30