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 $234.80   3.649%   $243.3679   $243.37   $243.35   $243.40  
  Purchase #2 $37.37   6.802%   $39.9119   $39.91   $39.90   $39.90  
  Purchase #3 $191.96   3.448%   $198.5788   $198.58   $198.60   $198.60  
  Purchase #4 $24.92   5.595%   $26.3143   $26.31   $26.30   $26.30  
  Purchase #5 $245.35   8.202%   $265.4736   $265.47   $265.45   $265.50  
  Purchase #6 $160.86   13.151%   $182.0147   $182.01   $182.00   $182.00  
  Purchase #7 $55.27   3.126%   $56.9977   $57.00   $57.00   $57.00  
  7 purchase totals = $950.53       $1,012.6589   $1,012.65   $1,012.60   $1,012.70