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 $55.25   12.671%   $62.2507   $62.25   $62.25   $62.30  
  Purchase #2 $184.72   6.589%   $196.8912   $196.89   $196.90   $196.90  
  Purchase #3 $23.65   8.381%   $25.6321   $25.63   $25.65   $25.60  
  Purchase #4 $21.59   11.674%   $24.1104   $24.11   $24.10   $24.10  
  Purchase #5 $88.44   4.213%   $92.166   $92.17   $92.15   $92.20  
  Purchase #6 $23.47   10.813%   $26.0078   $26.01   $26.00   $26.00  
  Purchase #7 $44.91   10.651%   $49.6934   $49.69   $49.70   $49.70  
  7 purchase totals = $442.03       $476.7516   $476.75   $476.75   $476.80