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 $70.36   10.523%   $77.764   $77.76   $77.75   $77.80  
  Purchase #2 $139.88   7.705%   $150.6578   $150.66   $150.65   $150.70  
  Purchase #3 $97.99   6.737%   $104.5916   $104.59   $104.60   $104.60  
  Purchase #4 $135.90   7.874%   $146.6008   $146.60   $146.60   $146.60  
  Purchase #5 $41.75   5.653%   $44.1101   $44.11   $44.10   $44.10  
  Purchase #6 $238.49   12.616%   $268.5779   $268.58   $268.60   $268.60  
  Purchase #7 $155.52   8.422%   $168.6179   $168.62   $168.60   $168.60  
  7 purchase totals = $879.89       $960.9201   $960.92   $960.90   $961.00