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 $38.66   6.474%   $41.1628   $41.16   $41.15   $41.20  
  Purchase #2 $240.65   10.471%   $265.8485   $265.85   $265.85   $265.80  
  Purchase #3 $221.99   12.177%   $249.0217   $249.02   $249.00   $249.00  
  Purchase #4 $61.31   7.108%   $65.6679   $65.67   $65.65   $65.70  
  Purchase #5 $83.78   4.621%   $87.6515   $87.65   $87.65   $87.70  
  Purchase #6 $152.69   4.446%   $159.4786   $159.48   $159.50   $159.50  
  Purchase #7 $75.88   8.193%   $82.0968   $82.10   $82.10   $82.10  
  7 purchase totals = $874.96       $950.9278   $950.93   $950.90   $951.00