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 $86.84   10.418%   $95.887   $95.89   $95.90   $95.90  
  Purchase #2 $61.63   5.560%   $65.0566   $65.06   $65.05   $65.10  
  Purchase #3 $100.32   12.126%   $112.4848   $112.48   $112.50   $112.50  
  Purchase #4 $41.99   4.270%   $43.783   $43.78   $43.80   $43.80  
  Purchase #5 $216.63   7.483%   $232.8404   $232.84   $232.85   $232.80  
  Purchase #6 $245.69   8.846%   $267.4237   $267.42   $267.40   $267.40  
  Purchase #7 $74.73   7.872%   $80.6127   $80.61   $80.60   $80.60  
  7 purchase totals = $827.83       $898.0882   $898.08   $898.10   $898.10