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 $222.34   8.598%   $241.4568   $241.46   $241.45   $241.50  
  Purchase #2 $73.90   8.807%   $80.4084   $80.41   $80.40   $80.40  
  Purchase #3 $245.67   10.190%   $270.7038   $270.70   $270.70   $270.70  
  Purchase #4 $173.46   8.540%   $188.2735   $188.27   $188.25   $188.30  
  Purchase #5 $46.28   12.846%   $52.2251   $52.23   $52.25   $52.20  
  Purchase #6 $80.47   5.167%   $84.6279   $84.63   $84.65   $84.60  
  Purchase #7 $174.71   5.220%   $183.8299   $183.83   $183.85   $183.80  
  7 purchase totals = $1,016.83       $1,101.5254   $1,101.53   $1,101.55   $1,101.50