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 $44.85   11.246%   $49.8938   $49.89   $49.90   $49.90  
  Purchase #2 $148.41   9.396%   $162.3546   $162.35   $162.35   $162.40  
  Purchase #3 $207.65   7.695%   $223.6287   $223.63   $223.65   $223.60  
  Purchase #4 $230.42   4.870%   $241.6415   $241.64   $241.65   $241.60  
  Purchase #5 $93.82   3.244%   $96.8635   $96.86   $96.85   $96.90  
  Purchase #6 $88.61   7.298%   $95.0768   $95.08   $95.10   $95.10  
  Purchase #7 $240.36   7.141%   $257.5241   $257.52   $257.50   $257.50  
  7 purchase totals = $1,054.12       $1,126.9830   $1,126.97   $1,127.00   $1,127.00