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 $223.98   12.758%   $252.5554   $252.56   $252.55   $252.60  
  Purchase #2 $166.94   11.413%   $185.9929   $185.99   $186.00   $186.00  
  Purchase #3 $134.47   5.247%   $141.5256   $141.53   $141.55   $141.50  
  Purchase #4 $61.88   5.399%   $65.2209   $65.22   $65.20   $65.20  
  Purchase #5 $198.53   4.184%   $206.8365   $206.84   $206.85   $206.80  
  Purchase #6 $222.58   4.767%   $233.1904   $233.19   $233.20   $233.20  
  Purchase #7 $153.93   12.290%   $172.848   $172.85   $172.85   $172.80  
  7 purchase totals = $1,162.31       $1,258.1697   $1,258.18   $1,258.20   $1,258.10