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 $91.36   7.847%   $98.529   $98.53   $98.55   $98.50  
  Purchase #2 $207.30   7.603%   $223.061   $223.06   $223.05   $223.10  
  Purchase #3 $197.71   12.536%   $222.4949   $222.49   $222.50   $222.50  
  Purchase #4 $144.84   8.793%   $157.5758   $157.58   $157.60   $157.60  
  Purchase #5 $100.98   8.130%   $109.1897   $109.19   $109.20   $109.20  
  Purchase #6 $43.88   9.370%   $47.9916   $47.99   $48.00   $48.00  
  Purchase #7 $120.37   13.814%   $136.9979   $137.00   $137.00   $137.00  
  7 purchase totals = $906.44       $995.8399   $995.84   $995.90   $995.90