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 $49.33   11.473%   $54.9896   $54.99   $55.00   $55.00  
  Purchase #2 $171.88   9.354%   $187.9577   $187.96   $187.95   $188.00  
  Purchase #3 $222.91   4.294%   $232.4818   $232.48   $232.50   $232.50  
  Purchase #4 $109.77   8.794%   $119.4232   $119.42   $119.40   $119.40  
  Purchase #5 $52.80   8.858%   $57.477   $57.48   $57.50   $57.50  
  Purchase #6 $88.80   3.614%   $92.0092   $92.01   $92.00   $92.00  
  Purchase #7 $240.66   13.696%   $273.6208   $273.62   $273.60   $273.60  
  7 purchase totals = $936.15       $1,017.9593   $1,017.96   $1,017.95   $1,018.00