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 $248.59   5.783%   $262.966   $262.97   $262.95   $263.00  
  Purchase #2 $70.57   9.481%   $77.2607   $77.26   $77.25   $77.30  
  Purchase #3 $62.89   4.518%   $65.7314   $65.73   $65.75   $65.70  
  Purchase #4 $168.52   12.682%   $189.8917   $189.89   $189.90   $189.90  
  Purchase #5 $137.79   9.501%   $150.8814   $150.88   $150.90   $150.90  
  Purchase #6 $85.28   13.202%   $96.5387   $96.54   $96.55   $96.50  
  Purchase #7 $214.55   9.433%   $234.7885   $234.79   $234.80   $234.80  
  7 purchase totals = $988.19       $1,078.0584   $1,078.06   $1,078.10   $1,078.10