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 $246.64   8.434%   $267.4416   $267.44   $267.45   $267.40  
  Purchase #2 $159.34   11.475%   $177.6243   $177.62   $177.60   $177.60  
  Purchase #3 $5.31   7.783%   $5.7233   $5.72   $5.70   $5.70  
  Purchase #4 $60.78   8.736%   $66.0897   $66.09   $66.10   $66.10  
  Purchase #5 $242.74   10.315%   $267.7786   $267.78   $267.80   $267.80  
  Purchase #6 $33.27   10.166%   $36.6522   $36.65   $36.65   $36.70  
  Purchase #7 $122.96   3.568%   $127.3472   $127.35   $127.35   $127.30  
  7 purchase totals = $871.04       $948.6569   $948.65   $948.65   $948.60