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 $245.30   9.531%   $268.6795   $268.68   $268.70   $268.70  
  Purchase #2 $15.30   4.454%   $15.9815   $15.98   $16.00   $16.00  
  Purchase #3 $78.30   3.592%   $81.1125   $81.11   $81.10   $81.10  
  Purchase #4 $226.43   10.224%   $249.5802   $249.58   $249.60   $249.60  
  Purchase #5 $115.75   3.342%   $119.6184   $119.62   $119.60   $119.60  
  Purchase #6 $52.85   7.677%   $56.9073   $56.91   $56.90   $56.90  
  Purchase #7 $216.78   12.147%   $243.1123   $243.11   $243.10   $243.10  
  7 purchase totals = $950.71       $1,034.9917   $1,034.99   $1,035.00   $1,035.00