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 $167.47   11.607%   $186.9082   $186.91   $186.90   $186.90  
  Purchase #2 $236.72   9.382%   $258.9291   $258.93   $258.95   $258.90  
  Purchase #3 $175.42   6.235%   $186.3574   $186.36   $186.35   $186.40  
  Purchase #4 $127.64   8.401%   $138.363   $138.36   $138.35   $138.40  
  Purchase #5 $212.88   11.119%   $236.5501   $236.55   $236.55   $236.60  
  Purchase #6 $232.53   7.271%   $249.4373   $249.44   $249.45   $249.40  
  Purchase #7 $88.81   10.472%   $98.1102   $98.11   $98.10   $98.10  
  7 purchase totals = $1,241.47       $1,354.6553   $1,354.66   $1,354.65   $1,354.70