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 $76.33   12.421%   $85.8109   $85.81   $85.80   $85.80  
  Purchase #2 $160.94   9.570%   $176.342   $176.34   $176.35   $176.30  
  Purchase #3 $53.51   7.850%   $57.7105   $57.71   $57.70   $57.70  
  Purchase #4 $193.53   3.551%   $200.4023   $200.40   $200.40   $200.40  
  Purchase #5 $163.63   5.460%   $172.5642   $172.56   $172.55   $172.60  
  Purchase #6 $88.31   4.382%   $92.1797   $92.18   $92.20   $92.20  
  Purchase #7 $224.83   5.666%   $237.5689   $237.57   $237.55   $237.60  
  7 purchase totals = $961.08       $1,022.5785   $1,022.57   $1,022.55   $1,022.60