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 $220.93   9.391%   $241.6775   $241.68   $241.70   $241.70  
  Purchase #2 $247.64   11.737%   $276.7055   $276.71   $276.70   $276.70  
  Purchase #3 $6.29   8.351%   $6.8153   $6.82   $6.80   $6.80  
  Purchase #4 $50.75   7.339%   $54.4745   $54.47   $54.45   $54.50  
  Purchase #5 $161.65   13.118%   $182.8552   $182.86   $182.85   $182.90  
  Purchase #6 $249.27   13.366%   $282.5874   $282.59   $282.60   $282.60  
  Purchase #7 $63.69   3.571%   $65.9644   $65.96   $65.95   $66.00  
  7 purchase totals = $1,000.22       $1,111.0798   $1,111.09   $1,111.05   $1,111.20