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 $95.75   7.477%   $102.9092   $102.91   $102.90   $102.90  
  Purchase #2 $217.31   11.748%   $242.8396   $242.84   $242.85   $242.80  
  Purchase #3 $75.61   6.523%   $80.542   $80.54   $80.55   $80.50  
  Purchase #4 $37.70   4.196%   $39.2819   $39.28   $39.30   $39.30  
  Purchase #5 $13.35   12.367%   $15.001   $15.00   $15.00   $15.00  
  Purchase #6 $69.35   6.202%   $73.6511   $73.65   $73.65   $73.70  
  Purchase #7 $192.56   13.227%   $218.0299   $218.03   $218.05   $218.00  
  7 purchase totals = $701.63       $772.2547   $772.25   $772.30   $772.20