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 $60.87   8.511%   $66.0506   $66.05   $66.05   $66.10  
  Purchase #2 $129.45   8.321%   $140.2215   $140.22   $140.20   $140.20  
  Purchase #3 $36.33   3.596%   $37.6364   $37.64   $37.65   $37.60  
  Purchase #4 $204.52   9.860%   $224.6857   $224.69   $224.70   $224.70  
  Purchase #5 $209.55   11.364%   $233.3633   $233.36   $233.35   $233.40  
  Purchase #6 $23.65   11.721%   $26.422   $26.42   $26.40   $26.40  
  Purchase #7 $131.84   4.445%   $137.7003   $137.70   $137.70   $137.70  
  7 purchase totals = $796.21       $866.0798   $866.08   $866.05   $866.10