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 $107.90   13.625%   $122.6014   $122.60   $122.60   $122.60  
  Purchase #2 $219.57   7.192%   $235.3615   $235.36   $235.35   $235.40  
  Purchase #3 $51.99   8.354%   $56.3332   $56.33   $56.35   $56.30  
  Purchase #4 $191.71   6.266%   $203.7225   $203.72   $203.70   $203.70  
  Purchase #5 $116.96   8.574%   $126.9882   $126.99   $127.00   $127.00  
  Purchase #6 $26.34   9.407%   $28.8178   $28.82   $28.80   $28.80  
  Purchase #7 $63.34   9.176%   $69.1521   $69.15   $69.15   $69.20  
  7 purchase totals = $777.81       $842.9767   $842.97   $842.95   $843.00