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 $232.73   5.834%   $246.3075   $246.31   $246.30   $246.30  
  Purchase #2 $90.52   13.819%   $103.029   $103.03   $103.05   $103.00  
  Purchase #3 $241.39   8.483%   $261.8671   $261.87   $261.85   $261.90  
  Purchase #4 $228.82   7.736%   $246.5215   $246.52   $246.50   $246.50  
  Purchase #5 $241.83   5.484%   $255.092   $255.09   $255.10   $255.10  
  Purchase #6 $11.76   4.234%   $12.2579   $12.26   $12.25   $12.30  
  Purchase #7 $103.65   11.442%   $115.5096   $115.51   $115.50   $115.50  
  7 purchase totals = $1,150.70       $1,240.5846   $1,240.59   $1,240.55   $1,240.60