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 $84.97   8.623%   $92.297   $92.30   $92.30   $92.30  
  Purchase #2 $15.95   8.610%   $17.3233   $17.32   $17.30   $17.30  
  Purchase #3 $64.67   8.300%   $70.0376   $70.04   $70.05   $70.00  
  Purchase #4 $82.74   12.863%   $93.3828   $93.38   $93.40   $93.40  
  Purchase #5 $76.71   11.594%   $85.6038   $85.60   $85.60   $85.60  
  Purchase #6 $59.66   6.189%   $63.3524   $63.35   $63.35   $63.40  
  Purchase #7 $27.61   8.832%   $30.0485   $30.05   $30.05   $30.00  
  7 purchase totals = $412.31       $452.0454   $452.04   $452.05   $452.00