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 $204.77   6.777%   $218.6473   $218.65   $218.65   $218.60  
  Purchase #2 $22.32   5.335%   $23.5108   $23.51   $23.50   $23.50  
  Purchase #3 $126.70   5.421%   $133.5684   $133.57   $133.55   $133.60  
  Purchase #4 $207.98   4.158%   $216.6278   $216.63   $216.65   $216.60  
  Purchase #5 $27.67   6.266%   $29.4038   $29.40   $29.40   $29.40  
  Purchase #6 $218.43   11.434%   $243.4053   $243.41   $243.40   $243.40  
  Purchase #7 $121.83   6.271%   $129.47   $129.47   $129.45   $129.50  
  7 purchase totals = $929.70       $994.6334   $994.64   $994.60   $994.60