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 $134.60   12.691%   $151.6821   $151.68   $151.70   $151.70  
  Purchase #2 $116.59   10.249%   $128.5393   $128.54   $128.55   $128.50  
  Purchase #3 $230.88   7.393%   $247.949   $247.95   $247.95   $247.90  
  Purchase #4 $82.69   8.826%   $89.9882   $89.99   $90.00   $90.00  
  Purchase #5 $185.73   8.278%   $201.1047   $201.10   $201.10   $201.10  
  Purchase #6 $76.55   12.600%   $86.1953   $86.20   $86.20   $86.20  
  Purchase #7 $150.97   4.517%   $157.7893   $157.79   $157.80   $157.80  
  7 purchase totals = $978.01       $1,063.2479   $1,063.25   $1,063.30   $1,063.20