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 $58.57   13.769%   $66.6345   $66.63   $66.65   $66.60  
  Purchase #2 $226.96   7.449%   $243.8663   $243.87   $243.85   $243.90  
  Purchase #3 $245.44   5.751%   $259.5553   $259.56   $259.55   $259.60  
  Purchase #4 $246.59   6.779%   $263.3063   $263.31   $263.30   $263.30  
  Purchase #5 $50.68   6.343%   $53.8946   $53.89   $53.90   $53.90  
  Purchase #6 $164.25   3.348%   $169.7491   $169.75   $169.75   $169.70  
  Purchase #7 $191.66   8.213%   $207.401   $207.40   $207.40   $207.40  
  7 purchase totals = $1,184.15       $1,264.4071   $1,264.41   $1,264.40   $1,264.40