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 $181.88   13.594%   $206.6048   $206.60   $206.60   $206.60  
  Purchase #2 $73.83   4.234%   $76.956   $76.96   $76.95   $77.00  
  Purchase #3 $109.42   3.724%   $113.4948   $113.49   $113.50   $113.50  
  Purchase #4 $183.65   9.707%   $201.4769   $201.48   $201.50   $201.50  
  Purchase #5 $99.99   5.361%   $105.3505   $105.35   $105.35   $105.40  
  Purchase #6 $6.83   11.311%   $7.6025   $7.60   $7.60   $7.60  
  Purchase #7 $139.70   4.540%   $146.0424   $146.04   $146.05   $146.00  
  7 purchase totals = $795.30       $857.5279   $857.52   $857.55   $857.60