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 $59.38   10.798%   $65.7919   $65.79   $65.80   $65.80  
  Purchase #2 $221.80   6.227%   $235.6115   $235.61   $235.60   $235.60  
  Purchase #3 $113.69   12.764%   $128.2014   $128.20   $128.20   $128.20  
  Purchase #4 $96.44   8.874%   $104.9981   $105.00   $105.00   $105.00  
  Purchase #5 $50.86   8.378%   $55.1211   $55.12   $55.10   $55.10  
  Purchase #6 $161.34   7.250%   $173.0372   $173.04   $173.05   $173.00  
  Purchase #7 $173.32   4.476%   $181.0778   $181.08   $181.10   $181.10  
  7 purchase totals = $876.83       $943.8390   $943.84   $943.85   $943.80