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 $89.66   6.502%   $95.4897   $95.49   $95.50   $95.50  
  Purchase #2 $16.25   3.264%   $16.7804   $16.78   $16.80   $16.80  
  Purchase #3 $19.73   13.652%   $22.4235   $22.42   $22.40   $22.40  
  Purchase #4 $211.93   4.844%   $222.1959   $222.20   $222.20   $222.20  
  Purchase #5 $9.43   11.730%   $10.5361   $10.54   $10.55   $10.50  
  Purchase #6 $152.75   13.792%   $173.8173   $173.82   $173.80   $173.80  
  Purchase #7 $41.86   7.798%   $45.1242   $45.12   $45.10   $45.10  
  7 purchase totals = $541.61       $586.3671   $586.37   $586.35   $586.30