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 $49.91   5.848%   $52.8287   $52.83   $52.85   $52.80  
  Purchase #2 $211.37   4.574%   $221.0381   $221.04   $221.05   $221.00  
  Purchase #3 $80.59   3.798%   $83.6508   $83.65   $83.65   $83.70  
  Purchase #4 $69.50   3.545%   $71.9638   $71.96   $71.95   $72.00  
  Purchase #5 $118.69   4.844%   $124.4393   $124.44   $124.45   $124.40  
  Purchase #6 $125.93   10.347%   $138.96   $138.96   $138.95   $139.00  
  Purchase #7 $60.44   4.666%   $63.2601   $63.26   $63.25   $63.30  
  7 purchase totals = $716.43       $756.1408   $756.14   $756.15   $756.20