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 $245.61   9.539%   $269.0387   $269.04   $269.05   $269.00  
  Purchase #2 $88.32   7.477%   $94.9237   $94.92   $94.90   $94.90  
  Purchase #3 $52.34   12.394%   $58.827   $58.83   $58.85   $58.80  
  Purchase #4 $246.25   12.222%   $276.3467   $276.35   $276.35   $276.30  
  Purchase #5 $43.43   10.595%   $48.0314   $48.03   $48.05   $48.00  
  Purchase #6 $201.73   10.676%   $223.2667   $223.27   $223.25   $223.30  
  Purchase #7 $171.42   6.277%   $182.18   $182.18   $182.20   $182.20  
  7 purchase totals = $1,049.10       $1,152.6142   $1,152.62   $1,152.65   $1,152.50