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 $68.96   7.589%   $74.1934   $74.19   $74.20   $74.20  
  Purchase #2 $122.97   12.199%   $137.9711   $137.97   $137.95   $138.00  
  Purchase #3 $49.33   9.256%   $53.896   $53.90   $53.90   $53.90  
  Purchase #4 $81.96   5.214%   $86.2334   $86.23   $86.25   $86.20  
  Purchase #5 $128.39   10.591%   $141.9878   $141.99   $142.00   $142.00  
  Purchase #6 $231.41   3.124%   $238.6392   $238.64   $238.65   $238.60  
  Purchase #7 $247.87   11.179%   $275.5794   $275.58   $275.60   $275.60  
  7 purchase totals = $930.89       $1,008.5003   $1,008.50   $1,008.55   $1,008.50