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 $220.39   12.132%   $247.1277   $247.13   $247.15   $247.10  
  Purchase #2 $234.99   5.391%   $247.6583   $247.66   $247.65   $247.70  
  Purchase #3 $61.94   13.491%   $70.2963   $70.30   $70.30   $70.30  
  Purchase #4 $68.46   13.615%   $77.7808   $77.78   $77.80   $77.80  
  Purchase #5 $68.43   8.565%   $74.291   $74.29   $74.30   $74.30  
  Purchase #6 $111.41   10.102%   $122.6646   $122.66   $122.65   $122.70  
  Purchase #7 $201.32   9.735%   $220.9185   $220.92   $220.90   $220.90  
  7 purchase totals = $966.94       $1,060.7372   $1,060.74   $1,060.75   $1,060.80