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 $161.76   11.278%   $180.0033   $180.00   $180.00   $180.00  
  Purchase #2 $132.64   9.545%   $145.3005   $145.30   $145.30   $145.30  
  Purchase #3 $225.45   7.202%   $241.6869   $241.69   $241.70   $241.70  
  Purchase #4 $5.90   5.222%   $6.2081   $6.21   $6.20   $6.20  
  Purchase #5 $108.90   12.122%   $122.1009   $122.10   $122.10   $122.10  
  Purchase #6 $11.43   10.345%   $12.6124   $12.61   $12.60   $12.60  
  Purchase #7 $61.65   4.751%   $64.579   $64.58   $64.60   $64.60  
  7 purchase totals = $707.73       $772.4911   $772.49   $772.50   $772.50