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 $58.81   8.414%   $63.7583   $63.76   $63.75   $63.80  
  Purchase #2 $40.46   8.737%   $43.995   $44.00   $44.00   $44.00  
  Purchase #3 $97.42   12.174%   $109.2799   $109.28   $109.30   $109.30  
  Purchase #4 $47.82   7.786%   $51.5433   $51.54   $51.55   $51.50  
  Purchase #5 $125.56   7.106%   $134.4823   $134.48   $134.50   $134.50  
  Purchase #6 $80.79   13.431%   $91.6409   $91.64   $91.65   $91.60  
  Purchase #7 $5.70   8.814%   $6.2024   $6.20   $6.20   $6.20  
  7 purchase totals = $456.56       $500.9021   $500.90   $500.95   $500.90