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 $235.70   12.373%   $264.8632   $264.86   $264.85   $264.90  
  Purchase #2 $50.43   6.461%   $53.6883   $53.69   $53.70   $53.70  
  Purchase #3 $113.35   5.333%   $119.395   $119.40   $119.40   $119.40  
  Purchase #4 $136.75   6.754%   $145.9861   $145.99   $146.00   $146.00  
  Purchase #5 $170.35   9.395%   $186.3544   $186.35   $186.35   $186.40  
  Purchase #6 $192.98   4.510%   $201.6834   $201.68   $201.70   $201.70  
  Purchase #7 $168.95   7.796%   $182.1213   $182.12   $182.10   $182.10  
  7 purchase totals = $1,068.51       $1,154.0917   $1,154.09   $1,154.10   $1,154.20