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 $112.78   9.726%   $123.749   $123.75   $123.75   $123.70  
  Purchase #2 $80.32   5.701%   $84.899   $84.90   $84.90   $84.90  
  Purchase #3 $216.71   5.198%   $227.9746   $227.97   $227.95   $228.00  
  Purchase #4 $24.60   13.720%   $27.9751   $27.98   $28.00   $28.00  
  Purchase #5 $202.70   6.762%   $216.4066   $216.41   $216.40   $216.40  
  Purchase #6 $178.67   7.557%   $192.1721   $192.17   $192.15   $192.20  
  Purchase #7 $144.85   10.196%   $159.6189   $159.62   $159.60   $159.60  
  7 purchase totals = $960.63       $1,032.7953   $1,032.80   $1,032.75   $1,032.80