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 $210.74   3.449%   $218.0084   $218.01   $218.00   $218.00  
  Purchase #2 $9.37   10.522%   $10.3559   $10.36   $10.35   $10.40  
  Purchase #3 $153.95   4.102%   $160.265   $160.27   $160.25   $160.30  
  Purchase #4 $77.80   7.682%   $83.7766   $83.78   $83.80   $83.80  
  Purchase #5 $5.86   3.219%   $6.0486   $6.05   $6.05   $6.00  
  Purchase #6 $168.43   9.513%   $184.4527   $184.45   $184.45   $184.50  
  Purchase #7 $175.82   5.816%   $186.0457   $186.05   $186.05   $186.00  
  7 purchase totals = $801.97       $848.9529   $848.97   $848.95   $849.00