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 $154.96   3.724%   $160.7307   $160.73   $160.75   $160.70  
  Purchase #2 $235.73   10.274%   $259.9489   $259.95   $259.95   $259.90  
  Purchase #3 $103.59   12.470%   $116.5077   $116.51   $116.50   $116.50  
  Purchase #4 $104.25   13.694%   $118.526   $118.53   $118.55   $118.50  
  Purchase #5 $231.60   6.367%   $246.346   $246.35   $246.35   $246.30  
  Purchase #6 $67.60   10.414%   $74.6399   $74.64   $74.65   $74.60  
  Purchase #7 $70.91   4.871%   $74.364   $74.36   $74.35   $74.40  
  7 purchase totals = $968.64       $1,051.0632   $1,051.07   $1,051.10   $1,050.90