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 $59.74   8.286%   $64.6901   $64.69   $64.70   $64.70  
  Purchase #2 $122.81   8.360%   $133.0769   $133.08   $133.10   $133.10  
  Purchase #3 $126.97   3.408%   $131.2971   $131.30   $131.30   $131.30  
  Purchase #4 $89.74   10.226%   $98.9168   $98.92   $98.90   $98.90  
  Purchase #5 $249.27   11.163%   $277.096   $277.10   $277.10   $277.10  
  Purchase #6 $249.52   8.454%   $270.6144   $270.61   $270.60   $270.60  
  Purchase #7 $240.61   4.299%   $250.9538   $250.95   $250.95   $251.00  
  7 purchase totals = $1,138.66       $1,226.6451   $1,226.65   $1,226.65   $1,226.70