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 $193.60   5.595%   $204.4319   $204.43   $204.45   $204.40  
  Purchase #2 $171.81   9.342%   $187.8605   $187.86   $187.85   $187.90  
  Purchase #3 $114.98   8.633%   $124.9062   $124.91   $124.90   $124.90  
  Purchase #4 $136.58   12.223%   $153.2742   $153.27   $153.25   $153.30  
  Purchase #5 $200.88   10.751%   $222.4766   $222.48   $222.50   $222.50  
  Purchase #6 $66.37   3.266%   $68.5376   $68.54   $68.55   $68.50  
  Purchase #7 $67.25   12.438%   $75.6146   $75.61   $75.60   $75.60  
  7 purchase totals = $951.47       $1,037.1016   $1,037.10   $1,037.10   $1,037.10