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 $196.71   3.356%   $203.3116   $203.31   $203.30   $203.30  
  Purchase #2 $236.87   9.784%   $260.0454   $260.05   $260.05   $260.00  
  Purchase #3 $53.47   12.471%   $60.1382   $60.14   $60.15   $60.10  
  Purchase #4 $164.95   7.677%   $177.6132   $177.61   $177.60   $177.60  
  Purchase #5 $111.78   5.463%   $117.8865   $117.89   $117.90   $117.90  
  Purchase #6 $29.41   8.404%   $31.8816   $31.88   $31.90   $31.90  
  Purchase #7 $187.82   10.849%   $208.1966   $208.20   $208.20   $208.20  
  7 purchase totals = $981.01       $1,059.0731   $1,059.08   $1,059.10   $1,059.00