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 $60.56   13.206%   $68.5576   $68.56   $68.55   $68.60  
  Purchase #2 $53.92   5.278%   $56.7659   $56.77   $56.75   $56.80  
  Purchase #3 $47.49   10.621%   $52.5339   $52.53   $52.55   $52.50  
  Purchase #4 $154.32   13.601%   $175.3091   $175.31   $175.30   $175.30  
  Purchase #5 $116.54   10.485%   $128.7592   $128.76   $128.75   $128.80  
  Purchase #6 $145.81   10.202%   $160.6855   $160.69   $160.70   $160.70  
  Purchase #7 $192.62   13.695%   $218.9993   $219.00   $219.00   $219.00  
  7 purchase totals = $771.26       $861.6105   $861.62   $861.60   $861.70