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 $56.95   8.155%   $61.5943   $61.59   $61.60   $61.60  
  Purchase #2 $22.90   8.761%   $24.9063   $24.91   $24.90   $24.90  
  Purchase #3 $189.43   3.376%   $195.8252   $195.83   $195.85   $195.80  
  Purchase #4 $187.46   3.857%   $194.6903   $194.69   $194.70   $194.70  
  Purchase #5 $55.43   5.663%   $58.569   $58.57   $58.55   $58.60  
  Purchase #6 $179.80   12.324%   $201.9586   $201.96   $201.95   $202.00  
  Purchase #7 $107.53   8.538%   $116.7109   $116.71   $116.70   $116.70  
  7 purchase totals = $799.50       $854.2546   $854.26   $854.25   $854.30