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 $49.26   10.604%   $54.4835   $54.48   $54.50   $54.50  
  Purchase #2 $236.64   12.365%   $265.9005   $265.90   $265.90   $265.90  
  Purchase #3 $191.28   8.244%   $207.0491   $207.05   $207.05   $207.00  
  Purchase #4 $192.52   11.271%   $214.2189   $214.22   $214.20   $214.20  
  Purchase #5 $24.77   8.165%   $26.7925   $26.79   $26.80   $26.80  
  Purchase #6 $223.58   8.363%   $242.278   $242.28   $242.30   $242.30  
  Purchase #7 $60.63   3.525%   $62.7672   $62.77   $62.75   $62.80  
  7 purchase totals = $978.68       $1,073.4897   $1,073.49   $1,073.50   $1,073.50