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 $38.39   12.854%   $43.3247   $43.32   $43.30   $43.30  
  Purchase #2 $187.83   11.235%   $208.9327   $208.93   $208.95   $208.90  
  Purchase #3 $64.44   6.641%   $68.7195   $68.72   $68.70   $68.70  
  Purchase #4 $249.87   13.755%   $284.2396   $284.24   $284.25   $284.20  
  Purchase #5 $106.99   9.640%   $117.3038   $117.30   $117.30   $117.30  
  Purchase #6 $215.95   4.183%   $224.9832   $224.98   $225.00   $225.00  
  Purchase #7 $102.52   10.852%   $113.6455   $113.65   $113.65   $113.60  
  7 purchase totals = $965.99       $1,061.1490   $1,061.14   $1,061.15   $1,061.00