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 $43.73   6.432%   $46.5427   $46.54   $46.55   $46.50  
  Purchase #2 $221.52   13.777%   $252.0388   $252.04   $252.05   $252.00  
  Purchase #3 $247.62   6.405%   $263.4801   $263.48   $263.50   $263.50  
  Purchase #4 $189.65   6.257%   $201.5164   $201.52   $201.50   $201.50  
  Purchase #5 $138.58   12.676%   $156.1464   $156.15   $156.15   $156.10  
  Purchase #6 $243.90   9.246%   $266.451   $266.45   $266.45   $266.50  
  Purchase #7 $137.52   3.326%   $142.0939   $142.09   $142.10   $142.10  
  7 purchase totals = $1,222.52       $1,328.2693   $1,328.27   $1,328.30   $1,328.20