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 $223.56   12.703%   $251.9588   $251.96   $251.95   $252.00  
  Purchase #2 $212.32   4.860%   $222.6388   $222.64   $222.65   $222.60  
  Purchase #3 $232.49   9.281%   $254.0674   $254.07   $254.05   $254.10  
  Purchase #4 $159.40   8.426%   $172.831   $172.83   $172.85   $172.80  
  Purchase #5 $91.88   13.757%   $104.5199   $104.52   $104.50   $104.50  
  Purchase #6 $154.61   5.104%   $162.5013   $162.50   $162.50   $162.50  
  Purchase #7 $31.29   8.719%   $34.0182   $34.02   $34.00   $34.00  
  7 purchase totals = $1,105.55       $1,202.5354   $1,202.54   $1,202.50   $1,202.50