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 $62.81   4.568%   $65.6792   $65.68   $65.70   $65.70  
  Purchase #2 $199.54   13.786%   $227.0486   $227.05   $227.05   $227.00  
  Purchase #3 $194.32   7.790%   $209.4575   $209.46   $209.45   $209.50  
  Purchase #4 $12.99   6.191%   $13.7942   $13.79   $13.80   $13.80  
  Purchase #5 $52.34   8.651%   $56.8679   $56.87   $56.85   $56.90  
  Purchase #6 $124.50   10.313%   $137.3397   $137.34   $137.35   $137.30  
  Purchase #7 $68.48   10.337%   $75.5588   $75.56   $75.55   $75.60  
  7 purchase totals = $714.98       $785.7459   $785.75   $785.75   $785.80