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 $87.85   10.133%   $96.7518   $96.75   $96.75   $96.80  
  Purchase #2 $122.44   13.455%   $138.9143   $138.91   $138.90   $138.90  
  Purchase #3 $179.93   10.123%   $198.1443   $198.14   $198.15   $198.10  
  Purchase #4 $43.90   7.707%   $47.2834   $47.28   $47.30   $47.30  
  Purchase #5 $53.69   12.398%   $60.3465   $60.35   $60.35   $60.30  
  Purchase #6 $236.69   8.483%   $256.7684   $256.77   $256.75   $256.80  
  Purchase #7 $191.59   12.403%   $215.3529   $215.35   $215.35   $215.40  
  7 purchase totals = $916.09       $1,013.5616   $1,013.55   $1,013.55   $1,013.60