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 $206.52   13.641%   $234.6914   $234.69   $234.70   $234.70  
  Purchase #2 $178.29   8.458%   $193.3698   $193.37   $193.35   $193.40  
  Purchase #3 $53.51   12.650%   $60.279   $60.28   $60.30   $60.30  
  Purchase #4 $150.99   5.163%   $158.7856   $158.79   $158.80   $158.80  
  Purchase #5 $18.84   11.746%   $21.0529   $21.05   $21.05   $21.10  
  Purchase #6 $232.47   3.297%   $240.1345   $240.13   $240.15   $240.10  
  Purchase #7 $131.84   3.228%   $136.0958   $136.10   $136.10   $136.10  
  7 purchase totals = $972.46       $1,044.4090   $1,044.41   $1,044.45   $1,044.50