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 $237.39   12.630%   $267.3724   $267.37   $267.35   $267.40  
  Purchase #2 $242.95   7.701%   $261.6596   $261.66   $261.65   $261.70  
  Purchase #3 $224.69   6.282%   $238.805   $238.81   $238.80   $238.80  
  Purchase #4 $29.31   5.220%   $30.84   $30.84   $30.85   $30.80  
  Purchase #5 $117.93   5.255%   $124.1272   $124.13   $124.15   $124.10  
  Purchase #6 $204.94   10.470%   $226.3972   $226.40   $226.40   $226.40  
  Purchase #7 $211.64   3.509%   $219.0664   $219.07   $219.05   $219.10  
  7 purchase totals = $1,268.85       $1,368.2678   $1,368.28   $1,368.25   $1,368.30