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 $47.93   8.236%   $51.8775   $51.88   $51.90   $51.90  
  Purchase #2 $110.28   13.159%   $124.7917   $124.79   $124.80   $124.80  
  Purchase #3 $24.46   6.163%   $25.9675   $25.97   $25.95   $26.00  
  Purchase #4 $56.76   8.103%   $61.3593   $61.36   $61.35   $61.40  
  Purchase #5 $68.47   7.661%   $73.7155   $73.72   $73.70   $73.70  
  Purchase #6 $69.40   9.202%   $75.7862   $75.79   $75.80   $75.80  
  Purchase #7 $66.75   3.591%   $69.147   $69.15   $69.15   $69.10  
  7 purchase totals = $444.05       $482.6447   $482.66   $482.65   $482.70