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 $60.93   3.541%   $63.0875   $63.09   $63.10   $63.10  
  Purchase #2 $138.56   3.602%   $143.5509   $143.55   $143.55   $143.60  
  Purchase #3 $246.62   3.847%   $256.1075   $256.11   $256.10   $256.10  
  Purchase #4 $90.74   3.178%   $93.6237   $93.62   $93.60   $93.60  
  Purchase #5 $166.39   13.222%   $188.3901   $188.39   $188.40   $188.40  
  Purchase #6 $52.63   4.818%   $55.1657   $55.17   $55.15   $55.20  
  Purchase #7 $185.98   6.772%   $198.5746   $198.57   $198.55   $198.60  
  7 purchase totals = $941.85       $998.5000   $998.50   $998.45   $998.60