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 $31.77   7.797%   $34.2471   $34.25   $34.25   $34.20  
  Purchase #2 $182.83   6.702%   $195.0833   $195.08   $195.10   $195.10  
  Purchase #3 $151.86   13.168%   $171.8569   $171.86   $171.85   $171.90  
  Purchase #4 $115.36   5.381%   $121.5675   $121.57   $121.55   $121.60  
  Purchase #5 $164.57   12.591%   $185.291   $185.29   $185.30   $185.30  
  Purchase #6 $212.49   5.416%   $223.9985   $224.00   $224.00   $224.00  
  Purchase #7 $23.47   6.495%   $24.9944   $24.99   $25.00   $25.00  
  7 purchase totals = $882.35       $957.0387   $957.04   $957.05   $957.10