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 $60.35   11.740%   $67.4351   $67.44   $67.45   $67.40  
  Purchase #2 $16.58   12.159%   $18.596   $18.60   $18.60   $18.60  
  Purchase #3 $47.75   4.693%   $49.9909   $49.99   $50.00   $50.00  
  Purchase #4 $241.65   9.866%   $265.4912   $265.49   $265.50   $265.50  
  Purchase #5 $115.87   5.464%   $122.2011   $122.20   $122.20   $122.20  
  Purchase #6 $113.46   6.136%   $120.4219   $120.42   $120.40   $120.40  
  Purchase #7 $146.30   3.800%   $151.8594   $151.86   $151.85   $151.90  
  7 purchase totals = $741.96       $795.9956   $796.00   $796.00   $796.00