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 $54.95   3.462%   $56.8524   $56.85   $56.85   $56.90  
  Purchase #2 $196.97   13.230%   $223.0291   $223.03   $223.05   $223.00  
  Purchase #3 $32.83   6.802%   $35.0631   $35.06   $35.05   $35.10  
  Purchase #4 $224.94   6.770%   $240.1684   $240.17   $240.15   $240.20  
  Purchase #5 $115.93   8.822%   $126.1573   $126.16   $126.15   $126.20  
  Purchase #6 $204.52   13.654%   $232.4452   $232.45   $232.45   $232.40  
  Purchase #7 $76.35   13.114%   $86.3625   $86.36   $86.35   $86.40  
  7 purchase totals = $906.49       $1,000.0780   $1,000.08   $1,000.05   $1,000.20