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 $232.25   4.666%   $243.0868   $243.09   $243.10   $243.10  
  Purchase #2 $242.79   4.184%   $252.9483   $252.95   $252.95   $252.90  
  Purchase #3 $97.25   4.502%   $101.6282   $101.63   $101.65   $101.60  
  Purchase #4 $152.39   12.773%   $171.8548   $171.85   $171.85   $171.90  
  Purchase #5 $183.87   4.594%   $192.317   $192.32   $192.30   $192.30  
  Purchase #6 $22.63   13.304%   $25.6407   $25.64   $25.65   $25.60  
  Purchase #7 $51.26   13.797%   $58.3323   $58.33   $58.35   $58.30  
  7 purchase totals = $982.44       $1,045.8081   $1,045.81   $1,045.85   $1,045.70