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 $58.47   6.122%   $62.0495   $62.05   $62.05   $62.00  
  Purchase #2 $38.50   7.385%   $41.3432   $41.34   $41.35   $41.30  
  Purchase #3 $31.70   12.301%   $35.5994   $35.60   $35.60   $35.60  
  Purchase #4 $151.58   11.291%   $168.6949   $168.69   $168.70   $168.70  
  Purchase #5 $25.31   5.242%   $26.6368   $26.64   $26.65   $26.60  
  Purchase #6 $202.46   11.210%   $225.1558   $225.16   $225.15   $225.20  
  Purchase #7 $51.77   11.248%   $57.5931   $57.59   $57.60   $57.60  
  7 purchase totals = $559.79       $617.0727   $617.07   $617.10   $617.00