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 $82.29   7.595%   $88.5399   $88.54   $88.55   $88.50  
  Purchase #2 $179.81   10.504%   $198.6972   $198.70   $198.70   $198.70  
  Purchase #3 $12.65   5.870%   $13.3926   $13.39   $13.40   $13.40  
  Purchase #4 $182.41   12.392%   $205.0142   $205.01   $205.00   $205.00  
  Purchase #5 $15.37   11.792%   $17.1824   $17.18   $17.20   $17.20  
  Purchase #6 $172.99   5.612%   $182.6982   $182.70   $182.70   $182.70  
  Purchase #7 $249.30   5.644%   $263.3705   $263.37   $263.35   $263.40  
  7 purchase totals = $894.82       $968.8950   $968.89   $968.90   $968.90