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 $224.84   9.823%   $246.926   $246.93   $246.95   $246.90  
  Purchase #2 $124.52   12.418%   $139.9829   $139.98   $140.00   $140.00  
  Purchase #3 $151.38   13.153%   $171.291   $171.29   $171.30   $171.30  
  Purchase #4 $207.32   13.631%   $235.5798   $235.58   $235.60   $235.60  
  Purchase #5 $173.36   4.791%   $181.6657   $181.67   $181.65   $181.70  
  Purchase #6 $75.54   8.648%   $82.0727   $82.07   $82.05   $82.10  
  Purchase #7 $220.89   7.771%   $238.0554   $238.06   $238.05   $238.10  
  7 purchase totals = $1,177.85       $1,295.5735   $1,295.58   $1,295.60   $1,295.70