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 $25.49   3.226%   $26.3123   $26.31   $26.30   $26.30  
  Purchase #2 $64.30   3.608%   $66.6199   $66.62   $66.60   $66.60  
  Purchase #3 $155.71   13.361%   $176.5144   $176.51   $176.50   $176.50  
  Purchase #4 $136.37   11.583%   $152.1657   $152.17   $152.15   $152.20  
  Purchase #5 $108.70   8.498%   $117.9373   $117.94   $117.95   $117.90  
  Purchase #6 $237.76   9.671%   $260.7538   $260.75   $260.75   $260.80  
  Purchase #7 $191.52   9.479%   $209.6742   $209.67   $209.65   $209.70  
  7 purchase totals = $919.85       $1,009.9776   $1,009.97   $1,009.90   $1,010.00