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 $56.94   7.737%   $61.3454   $61.35   $61.35   $61.30  
  Purchase #2 $6.34   8.371%   $6.8707   $6.87   $6.85   $6.90  
  Purchase #3 $213.38   4.809%   $223.6414   $223.64   $223.65   $223.60  
  Purchase #4 $49.50   9.782%   $54.3421   $54.34   $54.35   $54.30  
  Purchase #5 $175.43   9.655%   $192.3678   $192.37   $192.35   $192.40  
  Purchase #6 $122.72   10.805%   $135.9799   $135.98   $136.00   $136.00  
  Purchase #7 $79.84   3.784%   $82.8611   $82.86   $82.85   $82.90  
  7 purchase totals = $704.15       $757.4084   $757.41   $757.40   $757.40