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 $8.94   11.830%   $9.9976   $10.00   $10.00   $10.00  
  Purchase #2 $181.54   4.410%   $189.5459   $189.55   $189.55   $189.50  
  Purchase #3 $161.33   4.581%   $168.7205   $168.72   $168.70   $168.70  
  Purchase #4 $33.29   13.847%   $37.8997   $37.90   $37.90   $37.90  
  Purchase #5 $89.63   6.619%   $95.5626   $95.56   $95.55   $95.60  
  Purchase #6 $116.30   5.645%   $122.8651   $122.87   $122.85   $122.90  
  Purchase #7 $10.72   9.559%   $11.7447   $11.74   $11.75   $11.70  
  7 purchase totals = $601.75       $636.3361   $636.34   $636.30   $636.30