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 $22.94   4.174%   $23.8975   $23.90   $23.90   $23.90  
  Purchase #2 $173.55   6.603%   $185.0095   $185.01   $185.00   $185.00  
  Purchase #3 $152.54   4.268%   $159.0504   $159.05   $159.05   $159.10  
  Purchase #4 $233.98   13.255%   $264.994   $264.99   $265.00   $265.00  
  Purchase #5 $34.72   9.830%   $38.133   $38.13   $38.15   $38.10  
  Purchase #6 $230.41   7.200%   $246.9995   $247.00   $247.00   $247.00  
  Purchase #7 $215.64   9.331%   $235.7614   $235.76   $235.75   $235.80  
  7 purchase totals = $1,063.78       $1,153.8453   $1,153.84   $1,153.85   $1,153.90