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 $125.61   12.416%   $141.2057   $141.21   $141.20   $141.20  
  Purchase #2 $210.95   3.764%   $218.8902   $218.89   $218.90   $218.90  
  Purchase #3 $242.86   12.526%   $273.2806   $273.28   $273.30   $273.30  
  Purchase #4 $247.90   8.248%   $268.3468   $268.35   $268.35   $268.30  
  Purchase #5 $34.98   11.520%   $39.0097   $39.01   $39.00   $39.00  
  Purchase #6 $71.49   4.115%   $74.4318   $74.43   $74.45   $74.40  
  Purchase #7 $211.33   4.662%   $221.1822   $221.18   $221.20   $221.20  
  7 purchase totals = $1,145.12       $1,236.3470   $1,236.35   $1,236.40   $1,236.30