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 $65.65   7.586%   $70.6302   $70.63   $70.65   $70.60  
  Purchase #2 $181.91   10.554%   $201.1088   $201.11   $201.10   $201.10  
  Purchase #3 $35.53   5.490%   $37.4806   $37.48   $37.50   $37.50  
  Purchase #4 $235.62   6.745%   $251.5126   $251.51   $251.50   $251.50  
  Purchase #5 $132.75   13.594%   $150.796   $150.80   $150.80   $150.80  
  Purchase #6 $70.37   12.210%   $78.9622   $78.96   $78.95   $79.00  
  Purchase #7 $56.41   3.874%   $58.5953   $58.60   $58.60   $58.60  
  7 purchase totals = $778.24       $849.0857   $849.09   $849.10   $849.10