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 $96.57   13.595%   $109.6987   $109.70   $109.70   $109.70  
  Purchase #2 $128.91   9.346%   $140.9579   $140.96   $140.95   $141.00  
  Purchase #3 $175.32   11.324%   $195.1732   $195.17   $195.15   $195.20  
  Purchase #4 $77.61   6.130%   $82.3675   $82.37   $82.35   $82.40  
  Purchase #5 $173.25   13.488%   $196.618   $196.62   $196.60   $196.60  
  Purchase #6 $106.96   11.442%   $119.1984   $119.20   $119.20   $119.20  
  Purchase #7 $68.33   3.279%   $70.5705   $70.57   $70.55   $70.60  
  7 purchase totals = $826.95       $914.5842   $914.59   $914.50   $914.70