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 $149.94   9.147%   $163.655   $163.66   $163.65   $163.70  
  Purchase #2 $242.85   13.384%   $275.353   $275.35   $275.35   $275.40  
  Purchase #3 $58.74   7.841%   $63.3458   $63.35   $63.35   $63.30  
  Purchase #4 $162.99   7.322%   $174.9241   $174.92   $174.90   $174.90  
  Purchase #5 $243.35   10.577%   $269.0891   $269.09   $269.10   $269.10  
  Purchase #6 $248.89   4.560%   $260.2394   $260.24   $260.25   $260.20  
  Purchase #7 $173.43   6.549%   $184.7879   $184.79   $184.80   $184.80  
  7 purchase totals = $1,280.19       $1,391.3943   $1,391.40   $1,391.40   $1,391.40