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 $66.88   3.722%   $69.3693   $69.37   $69.35   $69.40  
  Purchase #2 $94.28   8.780%   $102.5578   $102.56   $102.55   $102.60  
  Purchase #3 $13.80   8.148%   $14.9244   $14.92   $14.90   $14.90  
  Purchase #4 $70.87   8.387%   $76.8139   $76.81   $76.80   $76.80  
  Purchase #5 $31.66   12.768%   $35.7023   $35.70   $35.70   $35.70  
  Purchase #6 $211.91   10.754%   $234.6988   $234.70   $234.70   $234.70  
  Purchase #7 $247.80   4.777%   $259.6374   $259.64   $259.65   $259.60  
  7 purchase totals = $737.20       $793.7039   $793.70   $793.65   $793.70