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 $250.78   5.740%   $265.1748   $265.17   $265.15   $265.20  
  Purchase #2 $113.40   8.169%   $122.6636   $122.66   $122.65   $122.70  
  Purchase #3 $86.35   13.823%   $98.2862   $98.29   $98.30   $98.30  
  Purchase #4 $11.44   3.218%   $11.8081   $11.81   $11.80   $11.80  
  Purchase #5 $24.97   7.385%   $26.814   $26.81   $26.80   $26.80  
  Purchase #6 $19.52   6.306%   $20.7509   $20.75   $20.75   $20.80  
  Purchase #7 $68.79   13.155%   $77.8393   $77.84   $77.85   $77.80  
  7 purchase totals = $575.25       $623.3369   $623.33   $623.30   $623.40