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 $64.42   7.140%   $69.0196   $69.02   $69.00   $69.00  
  Purchase #2 $98.98   6.786%   $105.6968   $105.70   $105.70   $105.70  
  Purchase #3 $87.29   5.359%   $91.9679   $91.97   $91.95   $92.00  
  Purchase #4 $7.62   6.680%   $8.129   $8.13   $8.15   $8.10  
  Purchase #5 $155.48   3.473%   $160.8798   $160.88   $160.90   $160.90  
  Purchase #6 $143.50   13.374%   $162.6917   $162.69   $162.70   $162.70  
  Purchase #7 $241.25   9.647%   $264.5234   $264.52   $264.50   $264.50  
  7 purchase totals = $798.54       $862.9082   $862.91   $862.90   $862.90