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 $192.61   9.867%   $211.6148   $211.61   $211.60   $211.60  
  Purchase #2 $62.77   6.825%   $67.0541   $67.05   $67.05   $67.10  
  Purchase #3 $212.36   10.174%   $233.9655   $233.97   $233.95   $234.00  
  Purchase #4 $20.30   4.381%   $21.1893   $21.19   $21.20   $21.20  
  Purchase #5 $84.94   6.729%   $90.6556   $90.66   $90.65   $90.70  
  Purchase #6 $124.31   7.718%   $133.9042   $133.90   $133.90   $133.90  
  Purchase #7 $132.69   9.654%   $145.4999   $145.50   $145.50   $145.50  
  7 purchase totals = $829.98       $903.8834   $903.88   $903.85   $904.00