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 $65.39   13.524%   $74.2333   $74.23   $74.25   $74.20  
  Purchase #2 $168.51   4.675%   $176.3878   $176.39   $176.40   $176.40  
  Purchase #3 $39.87   10.360%   $44.0005   $44.00   $44.00   $44.00  
  Purchase #4 $70.42   12.566%   $79.269   $79.27   $79.25   $79.30  
  Purchase #5 $23.72   11.865%   $26.5344   $26.53   $26.55   $26.50  
  Purchase #6 $64.25   5.165%   $67.5685   $67.57   $67.55   $67.60  
  Purchase #7 $103.44   7.513%   $111.2114   $111.21   $111.20   $111.20  
  7 purchase totals = $535.60       $579.2049   $579.20   $579.20   $579.20