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 $61.27   11.386%   $68.2462   $68.25   $68.25   $68.20  
  Purchase #2 $13.81   12.291%   $15.5074   $15.51   $15.50   $15.50  
  Purchase #3 $11.57   7.546%   $12.4431   $12.44   $12.45   $12.40  
  Purchase #4 $232.66   8.684%   $252.8642   $252.86   $252.85   $252.90  
  Purchase #5 $46.35   4.567%   $48.4668   $48.47   $48.45   $48.50  
  Purchase #6 $150.39   11.419%   $167.563   $167.56   $167.55   $167.60  
  Purchase #7 $219.31   7.386%   $235.5082   $235.51   $235.50   $235.50  
  7 purchase totals = $735.36       $800.5989   $800.60   $800.55   $800.60