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 $217.56   13.702%   $247.3701   $247.37   $247.35   $247.40  
  Purchase #2 $52.93   12.538%   $59.5664   $59.57   $59.55   $59.60  
  Purchase #3 $8.39   4.847%   $8.7967   $8.80   $8.80   $8.80  
  Purchase #4 $52.62   13.571%   $59.7611   $59.76   $59.75   $59.80  
  Purchase #5 $158.84   4.490%   $165.9719   $165.97   $165.95   $166.00  
  Purchase #6 $156.63   4.247%   $163.2821   $163.28   $163.30   $163.30  
  Purchase #7 $229.59   10.544%   $253.798   $253.80   $253.80   $253.80  
  7 purchase totals = $876.56       $958.5463   $958.55   $958.50   $958.70