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 $247.84   11.106%   $275.3651   $275.37   $275.35   $275.40  
  Purchase #2 $206.58   9.840%   $226.9075   $226.91   $226.90   $226.90  
  Purchase #3 $152.60   10.419%   $168.4994   $168.50   $168.50   $168.50  
  Purchase #4 $240.49   4.365%   $250.9874   $250.99   $251.00   $251.00  
  Purchase #5 $74.63   7.633%   $80.3265   $80.33   $80.35   $80.30  
  Purchase #6 $234.76   9.425%   $256.8861   $256.89   $256.90   $256.90  
  Purchase #7 $43.85   5.726%   $46.3609   $46.36   $46.35   $46.40  
  7 purchase totals = $1,200.75       $1,305.3329   $1,305.35   $1,305.35   $1,305.40