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 $52.55   10.343%   $57.9852   $57.99   $58.00   $58.00  
  Purchase #2 $25.97   6.194%   $27.5786   $27.58   $27.60   $27.60  
  Purchase #3 $234.66   11.281%   $261.132   $261.13   $261.15   $261.10  
  Purchase #4 $160.99   8.331%   $174.4021   $174.40   $174.40   $174.40  
  Purchase #5 $244.74   12.389%   $275.0608   $275.06   $275.05   $275.10  
  Purchase #6 $119.27   5.453%   $125.7738   $125.77   $125.75   $125.80  
  Purchase #7 $231.74   7.263%   $248.5713   $248.57   $248.55   $248.60  
  7 purchase totals = $1,069.92       $1,170.5038   $1,170.50   $1,170.50   $1,170.60