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 $9.70   11.552%   $10.8205   $10.82   $10.80   $10.80  
  Purchase #2 $5.58   5.756%   $5.9012   $5.90   $5.90   $5.90  
  Purchase #3 $56.25   10.644%   $62.2373   $62.24   $62.25   $62.20  
  Purchase #4 $161.90   5.370%   $170.594   $170.59   $170.60   $170.60  
  Purchase #5 $28.32   8.482%   $30.7221   $30.72   $30.70   $30.70  
  Purchase #6 $64.72   8.147%   $69.9927   $69.99   $70.00   $70.00  
  Purchase #7 $47.53   5.329%   $50.0629   $50.06   $50.05   $50.10  
  7 purchase totals = $374.00       $400.3307   $400.32   $400.30   $400.30