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 $16.28   7.257%   $17.4614   $17.46   $17.45   $17.50  
  Purchase #2 $221.79   9.276%   $242.3632   $242.36   $242.35   $242.40  
  Purchase #3 $40.29   4.861%   $42.2485   $42.25   $42.25   $42.20  
  Purchase #4 $67.53   4.748%   $70.7363   $70.74   $70.75   $70.70  
  Purchase #5 $147.52   3.277%   $152.3542   $152.35   $152.35   $152.40  
  Purchase #6 $163.51   13.811%   $186.0924   $186.09   $186.10   $186.10  
  Purchase #7 $119.25   3.397%   $123.3009   $123.30   $123.30   $123.30  
  7 purchase totals = $776.17       $834.5569   $834.55   $834.55   $834.60