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 $61.35   12.638%   $69.1034   $69.10   $69.10   $69.10  
  Purchase #2 $193.83   3.531%   $200.6741   $200.67   $200.65   $200.70  
  Purchase #3 $186.34   11.332%   $207.456   $207.46   $207.45   $207.50  
  Purchase #4 $26.36   5.781%   $27.8839   $27.88   $27.90   $27.90  
  Purchase #5 $137.87   13.146%   $155.9944   $155.99   $156.00   $156.00  
  Purchase #6 $131.68   13.136%   $148.9775   $148.98   $149.00   $149.00  
  Purchase #7 $65.82   10.791%   $72.9226   $72.92   $72.90   $72.90  
  7 purchase totals = $803.25       $883.0119   $883.00   $883.00   $883.10