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 $191.35   7.651%   $205.9902   $205.99   $206.00   $206.00  
  Purchase #2 $23.69   8.641%   $25.7371   $25.74   $25.75   $25.70  
  Purchase #3 $95.57   4.506%   $99.8764   $99.88   $99.90   $99.90  
  Purchase #4 $177.52   13.640%   $201.7337   $201.73   $201.75   $201.70  
  Purchase #5 $5.26   7.838%   $5.6723   $5.67   $5.65   $5.70  
  Purchase #6 $219.46   5.713%   $231.9977   $232.00   $232.00   $232.00  
  Purchase #7 $78.82   13.341%   $89.3354   $89.34   $89.35   $89.30  
  7 purchase totals = $791.67       $860.3428   $860.35   $860.40   $860.30