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 $105.63   13.228%   $119.6027   $119.60   $119.60   $119.60  
  Purchase #2 $9.72   6.349%   $10.3371   $10.34   $10.35   $10.30  
  Purchase #3 $34.31   10.812%   $38.0196   $38.02   $38.00   $38.00  
  Purchase #4 $250.70   9.489%   $274.4889   $274.49   $274.50   $274.50  
  Purchase #5 $107.85   12.738%   $121.5879   $121.59   $121.60   $121.60  
  Purchase #6 $38.49   3.679%   $39.906   $39.91   $39.90   $39.90  
  Purchase #7 $179.25   4.544%   $187.3951   $187.40   $187.40   $187.40  
  7 purchase totals = $725.95       $791.3373   $791.35   $791.35   $791.30