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 $70.97   5.623%   $74.9606   $74.96   $74.95   $75.00  
  Purchase #2 $134.64   13.318%   $152.5714   $152.57   $152.55   $152.60  
  Purchase #3 $98.28   9.836%   $107.9468   $107.95   $107.95   $107.90  
  Purchase #4 $223.76   5.562%   $236.2055   $236.21   $236.20   $236.20  
  Purchase #5 $85.49   6.826%   $91.3255   $91.33   $91.35   $91.30  
  Purchase #6 $154.52   5.859%   $163.5733   $163.57   $163.55   $163.60  
  Purchase #7 $124.27   5.167%   $130.691   $130.69   $130.70   $130.70  
  7 purchase totals = $891.93       $957.2741   $957.28   $957.25   $957.30