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 $49.36   8.540%   $53.5753   $53.58   $53.60   $53.60  
  Purchase #2 $58.38   12.335%   $65.5812   $65.58   $65.60   $65.60  
  Purchase #3 $84.57   12.218%   $94.9028   $94.90   $94.90   $94.90  
  Purchase #4 $61.28   9.633%   $67.1831   $67.18   $67.20   $67.20  
  Purchase #5 $71.76   4.724%   $75.1499   $75.15   $75.15   $75.10  
  Purchase #6 $237.38   13.553%   $269.5521   $269.55   $269.55   $269.60  
  Purchase #7 $215.62   7.607%   $232.0222   $232.02   $232.00   $232.00  
  7 purchase totals = $778.35       $857.9666   $857.96   $858.00   $858.00