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 $76.70   13.121%   $86.7638   $86.76   $86.75   $86.80  
  Purchase #2 $70.39   4.199%   $73.3457   $73.35   $73.35   $73.30  
  Purchase #3 $5.53   8.553%   $6.003   $6.00   $6.00   $6.00  
  Purchase #4 $212.45   6.830%   $226.9603   $226.96   $226.95   $227.00  
  Purchase #5 $21.90   9.818%   $24.0501   $24.05   $24.05   $24.10  
  Purchase #6 $34.46   9.268%   $37.6538   $37.65   $37.65   $37.70  
  Purchase #7 $98.35   9.626%   $107.8172   $107.82   $107.80   $107.80  
  7 purchase totals = $519.78       $562.5939   $562.59   $562.55   $562.70