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 $43.34   4.289%   $45.1989   $45.20   $45.20   $45.20  
  Purchase #2 $21.50   8.768%   $23.3851   $23.39   $23.40   $23.40  
  Purchase #3 $38.80   7.539%   $41.7251   $41.73   $41.75   $41.70  
  Purchase #4 $10.54   5.822%   $11.1536   $11.15   $11.15   $11.20  
  Purchase #5 $172.38   12.771%   $194.3946   $194.39   $194.40   $194.40  
  Purchase #6 $120.90   8.496%   $131.1717   $131.17   $131.15   $131.20  
  Purchase #7 $224.63   13.229%   $254.3463   $254.35   $254.35   $254.30  
  7 purchase totals = $632.09       $701.3753   $701.38   $701.40   $701.40