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 $176.72   5.395%   $186.254   $186.25   $186.25   $186.30  
  Purchase #2 $139.27   5.555%   $147.0064   $147.01   $147.00   $147.00  
  Purchase #3 $19.80   13.220%   $22.4176   $22.42   $22.40   $22.40  
  Purchase #4 $229.25   7.199%   $245.7537   $245.75   $245.75   $245.80  
  Purchase #5 $154.90   8.549%   $168.1424   $168.14   $168.15   $168.10  
  Purchase #6 $168.45   10.697%   $186.4691   $186.47   $186.45   $186.50  
  Purchase #7 $42.76   6.851%   $45.6895   $45.69   $45.70   $45.70  
  7 purchase totals = $931.15       $1,001.7327   $1,001.73   $1,001.70   $1,001.80