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 $141.66   10.787%   $156.9409   $156.94   $156.95   $156.90  
  Purchase #2 $159.82   3.508%   $165.4265   $165.43   $165.45   $165.40  
  Purchase #3 $70.58   8.148%   $76.3309   $76.33   $76.35   $76.30  
  Purchase #4 $241.89   10.290%   $266.7805   $266.78   $266.80   $266.80  
  Purchase #5 $97.44   9.618%   $106.8118   $106.81   $106.80   $106.80  
  Purchase #6 $25.98   9.337%   $28.4058   $28.41   $28.40   $28.40  
  Purchase #7 $226.69   10.151%   $249.7013   $249.70   $249.70   $249.70  
  7 purchase totals = $964.06       $1,050.3977   $1,050.40   $1,050.45   $1,050.30