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 $61.70   12.547%   $69.4415   $69.44   $69.45   $69.40  
  Purchase #2 $217.95   12.502%   $245.1981   $245.20   $245.20   $245.20  
  Purchase #3 $211.26   7.493%   $227.0897   $227.09   $227.10   $227.10  
  Purchase #4 $224.66   13.590%   $255.1913   $255.19   $255.20   $255.20  
  Purchase #5 $145.72   11.870%   $163.017   $163.02   $163.00   $163.00  
  Purchase #6 $198.95   8.637%   $216.1333   $216.13   $216.15   $216.10  
  Purchase #7 $90.25   11.180%   $100.34   $100.34   $100.35   $100.30  
  7 purchase totals = $1,150.49       $1,276.4109   $1,276.41   $1,276.45   $1,276.30