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 $234.44   12.261%   $263.1847   $263.18   $263.20   $263.20  
  Purchase #2 $29.87   11.147%   $33.1996   $33.20   $33.20   $33.20  
  Purchase #3 $192.53   13.475%   $218.4734   $218.47   $218.45   $218.50  
  Purchase #4 $56.59   5.452%   $59.6753   $59.68   $59.70   $59.70  
  Purchase #5 $86.99   5.115%   $91.4395   $91.44   $91.45   $91.40  
  Purchase #6 $213.25   5.353%   $224.6653   $224.67   $224.65   $224.70  
  Purchase #7 $176.83   8.131%   $191.208   $191.21   $191.20   $191.20  
  7 purchase totals = $990.50       $1,081.8458   $1,081.85   $1,081.85   $1,081.90