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 $36.41   13.807%   $41.4371   $41.44   $41.45   $41.40  
  Purchase #2 $119.42   11.530%   $133.1891   $133.19   $133.20   $133.20  
  Purchase #3 $127.68   4.800%   $133.8086   $133.81   $133.80   $133.80  
  Purchase #4 $179.89   11.475%   $200.5324   $200.53   $200.55   $200.50  
  Purchase #5 $177.67   3.368%   $183.6539   $183.65   $183.65   $183.70  
  Purchase #6 $193.76   9.130%   $211.4503   $211.45   $211.45   $211.50  
  Purchase #7 $90.39   4.617%   $94.5633   $94.56   $94.55   $94.60  
  7 purchase totals = $925.22       $998.6347   $998.63   $998.65   $998.70