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 $242.95   5.263%   $255.7365   $255.74   $255.75   $255.70  
  Purchase #2 $92.83   3.349%   $95.9389   $95.94   $95.95   $95.90  
  Purchase #3 $36.57   5.277%   $38.4998   $38.50   $38.50   $38.50  
  Purchase #4 $183.93   7.346%   $197.4415   $197.44   $197.45   $197.40  
  Purchase #5 $209.58   6.655%   $223.5275   $223.53   $223.55   $223.50  
  Purchase #6 $140.78   13.858%   $160.2893   $160.29   $160.30   $160.30  
  Purchase #7 $212.99   10.782%   $235.9546   $235.95   $235.95   $236.00  
  7 purchase totals = $1,119.63       $1,207.3881   $1,207.39   $1,207.45   $1,207.30