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 $84.43   13.759%   $96.0467   $96.05   $96.05   $96.00  
  Purchase #2 $78.97   10.511%   $87.2705   $87.27   $87.25   $87.30  
  Purchase #3 $77.78   6.551%   $82.8754   $82.88   $82.90   $82.90  
  Purchase #4 $56.28   6.850%   $60.1352   $60.14   $60.15   $60.10  
  Purchase #5 $201.38   4.277%   $209.993   $209.99   $210.00   $210.00  
  Purchase #6 $5.35   12.757%   $6.0325   $6.03   $6.05   $6.00  
  Purchase #7 $41.81   3.222%   $43.1571   $43.16   $43.15   $43.20  
  7 purchase totals = $546.00       $585.5104   $585.52   $585.55   $585.50