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 $235.90   10.106%   $259.7401   $259.74   $259.75   $259.70  
  Purchase #2 $180.98   6.827%   $193.3355   $193.34   $193.35   $193.30  
  Purchase #3 $139.66   7.372%   $149.9557   $149.96   $149.95   $150.00  
  Purchase #4 $65.43   3.281%   $67.5768   $67.58   $67.60   $67.60  
  Purchase #5 $96.60   7.847%   $104.1802   $104.18   $104.20   $104.20  
  Purchase #6 $124.63   10.773%   $138.0564   $138.06   $138.05   $138.10  
  Purchase #7 $56.95   10.275%   $62.8016   $62.80   $62.80   $62.80  
  7 purchase totals = $900.15       $975.6463   $975.66   $975.70   $975.70