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 $228.31   8.423%   $247.5406   $247.54   $247.55   $247.50  
  Purchase #2 $44.68   10.325%   $49.2932   $49.29   $49.30   $49.30  
  Purchase #3 $199.67   6.672%   $212.992   $212.99   $213.00   $213.00  
  Purchase #4 $22.50   5.619%   $23.7643   $23.76   $23.75   $23.80  
  Purchase #5 $216.57   4.770%   $226.9004   $226.90   $226.90   $226.90  
  Purchase #6 $184.87   7.697%   $199.0994   $199.10   $199.10   $199.10  
  Purchase #7 $55.41   10.214%   $61.0696   $61.07   $61.05   $61.10  
  7 purchase totals = $952.01       $1,020.6595   $1,020.65   $1,020.65   $1,020.70