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 $241.33   4.714%   $252.7063   $252.71   $252.70   $252.70  
  Purchase #2 $51.51   9.353%   $56.3277   $56.33   $56.35   $56.30  
  Purchase #3 $207.62   13.370%   $235.3788   $235.38   $235.40   $235.40  
  Purchase #4 $83.81   8.693%   $91.0956   $91.10   $91.10   $91.10  
  Purchase #5 $182.97   5.227%   $192.5338   $192.53   $192.55   $192.50  
  Purchase #6 $19.52   13.608%   $22.1763   $22.18   $22.20   $22.20  
  Purchase #7 $180.66   10.181%   $199.053   $199.05   $199.05   $199.10  
  7 purchase totals = $967.42       $1,049.2715   $1,049.28   $1,049.35   $1,049.30