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 $60.39   4.375%   $63.0321   $63.03   $63.05   $63.00  
  Purchase #2 $207.66   13.644%   $235.9931   $235.99   $236.00   $236.00  
  Purchase #3 $99.61   6.232%   $105.8177   $105.82   $105.80   $105.80  
  Purchase #4 $7.77   6.288%   $8.2586   $8.26   $8.25   $8.30  
  Purchase #5 $60.50   7.795%   $65.216   $65.22   $65.20   $65.20  
  Purchase #6 $82.65   5.523%   $87.2148   $87.21   $87.20   $87.20  
  Purchase #7 $235.61   6.209%   $250.239   $250.24   $250.25   $250.20  
  7 purchase totals = $754.19       $815.7713   $815.77   $815.75   $815.70