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 $166.81   10.711%   $184.677   $184.68   $184.70   $184.70  
  Purchase #2 $215.30   4.483%   $224.9519   $224.95   $224.95   $225.00  
  Purchase #3 $57.34   3.285%   $59.2236   $59.22   $59.20   $59.20  
  Purchase #4 $150.76   6.492%   $160.5473   $160.55   $160.55   $160.50  
  Purchase #5 $62.76   11.654%   $70.0741   $70.07   $70.05   $70.10  
  Purchase #6 $9.88   4.672%   $10.3416   $10.34   $10.35   $10.30  
  Purchase #7 $56.27   4.594%   $58.855   $58.86   $58.85   $58.90  
  7 purchase totals = $719.12       $768.6705   $768.67   $768.65   $768.70