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 $88.43   11.454%   $98.5588   $98.56   $98.55   $98.60  
  Purchase #2 $143.56   13.196%   $162.5042   $162.50   $162.50   $162.50  
  Purchase #3 $190.29   9.139%   $207.6806   $207.68   $207.70   $207.70  
  Purchase #4 $231.26   8.178%   $250.1724   $250.17   $250.15   $250.20  
  Purchase #5 $96.93   13.437%   $109.9545   $109.95   $109.95   $110.00  
  Purchase #6 $75.62   12.786%   $85.2888   $85.29   $85.30   $85.30  
  Purchase #7 $103.51   5.864%   $109.5798   $109.58   $109.60   $109.60  
  7 purchase totals = $929.60       $1,023.7391   $1,023.73   $1,023.75   $1,023.90