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 $106.25   12.652%   $119.6928   $119.69   $119.70   $119.70  
  Purchase #2 $123.55   12.189%   $138.6095   $138.61   $138.60   $138.60  
  Purchase #3 $107.59   6.229%   $114.2918   $114.29   $114.30   $114.30  
  Purchase #4 $87.69   11.479%   $97.7559   $97.76   $97.75   $97.80  
  Purchase #5 $150.56   10.782%   $166.7934   $166.79   $166.80   $166.80  
  Purchase #6 $72.83   4.370%   $76.0127   $76.01   $76.00   $76.00  
  Purchase #7 $67.79   7.270%   $72.7183   $72.72   $72.70   $72.70  
  7 purchase totals = $716.26       $785.8744   $785.87   $785.85   $785.90