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 $54.53   4.582%   $57.0286   $57.03   $57.05   $57.00  
  Purchase #2 $57.63   5.471%   $60.7829   $60.78   $60.80   $60.80  
  Purchase #3 $66.84   3.328%   $69.0644   $69.06   $69.05   $69.10  
  Purchase #4 $151.89   13.706%   $172.708   $172.71   $172.70   $172.70  
  Purchase #5 $234.29   7.229%   $251.2268   $251.23   $251.25   $251.20  
  Purchase #6 $224.27   5.521%   $236.6519   $236.65   $236.65   $236.70  
  Purchase #7 $159.29   4.699%   $166.775   $166.78   $166.80   $166.80  
  7 purchase totals = $948.74       $1,014.2376   $1,014.24   $1,014.30   $1,014.30