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 $185.53   10.262%   $204.5691   $204.57   $204.55   $204.60  
  Purchase #2 $245.92   5.192%   $258.6882   $258.69   $258.70   $258.70  
  Purchase #3 $82.97   7.701%   $89.3595   $89.36   $89.35   $89.40  
  Purchase #4 $79.94   4.666%   $83.67   $83.67   $83.65   $83.70  
  Purchase #5 $177.79   6.340%   $189.0619   $189.06   $189.05   $189.10  
  Purchase #6 $186.96   6.288%   $198.716   $198.72   $198.70   $198.70  
  Purchase #7 $240.98   4.579%   $252.0145   $252.01   $252.00   $252.00  
  7 purchase totals = $1,200.09       $1,276.0792   $1,276.08   $1,276.00   $1,276.20