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 $195.75   6.622%   $208.7126   $208.71   $208.70   $208.70  
  Purchase #2 $141.35   12.734%   $159.3495   $159.35   $159.35   $159.30  
  Purchase #3 $78.81   5.633%   $83.2494   $83.25   $83.25   $83.20  
  Purchase #4 $183.48   3.705%   $190.2779   $190.28   $190.30   $190.30  
  Purchase #5 $197.93   9.289%   $216.3157   $216.32   $216.30   $216.30  
  Purchase #6 $189.50   9.481%   $207.4665   $207.47   $207.45   $207.50  
  Purchase #7 $75.26   6.293%   $79.9961   $80.00   $80.00   $80.00  
  7 purchase totals = $1,062.08       $1,145.3677   $1,145.38   $1,145.35   $1,145.30