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 $250.87   6.571%   $267.3547   $267.35   $267.35   $267.40  
  Purchase #2 $220.96   9.815%   $242.6472   $242.65   $242.65   $242.60  
  Purchase #3 $179.79   13.629%   $204.2936   $204.29   $204.30   $204.30  
  Purchase #4 $35.78   3.207%   $36.9275   $36.93   $36.95   $36.90  
  Purchase #5 $56.96   8.833%   $61.9913   $61.99   $62.00   $62.00  
  Purchase #6 $26.96   4.284%   $28.115   $28.12   $28.10   $28.10  
  Purchase #7 $248.67   10.332%   $274.3626   $274.36   $274.35   $274.40  
  7 purchase totals = $1,019.99       $1,115.6919   $1,115.69   $1,115.70   $1,115.70