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 $228.68   8.550%   $248.2321   $248.23   $248.25   $248.20  
  Purchase #2 $162.25   12.626%   $182.7357   $182.74   $182.75   $182.70  
  Purchase #3 $165.53   9.268%   $180.8713   $180.87   $180.85   $180.90  
  Purchase #4 $98.68   5.724%   $104.3284   $104.33   $104.35   $104.30  
  Purchase #5 $55.29   13.124%   $62.5463   $62.55   $62.55   $62.50  
  Purchase #6 $242.42   4.780%   $254.0077   $254.01   $254.00   $254.00  
  Purchase #7 $12.77   13.706%   $14.5203   $14.52   $14.50   $14.50  
  7 purchase totals = $965.62       $1,047.2418   $1,047.25   $1,047.25   $1,047.10