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 $61.52   7.671%   $66.2392   $66.24   $66.25   $66.20  
  Purchase #2 $178.89   7.560%   $192.4141   $192.41   $192.40   $192.40  
  Purchase #3 $175.80   11.119%   $195.3472   $195.35   $195.35   $195.30  
  Purchase #4 $239.91   13.619%   $272.5833   $272.58   $272.60   $272.60  
  Purchase #5 $72.73   7.401%   $78.1127   $78.11   $78.10   $78.10  
  Purchase #6 $153.64   7.119%   $164.5776   $164.58   $164.60   $164.60  
  Purchase #7 $245.52   13.269%   $278.098   $278.10   $278.10   $278.10  
  7 purchase totals = $1,128.01       $1,247.3721   $1,247.37   $1,247.40   $1,247.30