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 $32.43   12.669%   $36.5386   $36.54   $36.55   $36.50  
  Purchase #2 $193.95   5.690%   $204.9858   $204.99   $205.00   $205.00  
  Purchase #3 $238.55   12.791%   $269.0629   $269.06   $269.05   $269.10  
  Purchase #4 $24.50   10.740%   $27.1313   $27.13   $27.15   $27.10  
  Purchase #5 $70.89   13.241%   $80.2765   $80.28   $80.30   $80.30  
  Purchase #6 $195.59   9.407%   $213.9892   $213.99   $214.00   $214.00  
  Purchase #7 $224.76   6.181%   $238.6524   $238.65   $238.65   $238.70  
  7 purchase totals = $980.67       $1,070.6367   $1,070.64   $1,070.70   $1,070.70