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 $239.62   10.872%   $265.6715   $265.67   $265.65   $265.70  
  Purchase #2 $137.78   8.139%   $148.9939   $148.99   $149.00   $149.00  
  Purchase #3 $141.69   7.547%   $152.3833   $152.38   $152.40   $152.40  
  Purchase #4 $196.98   8.641%   $214.001   $214.00   $214.00   $214.00  
  Purchase #5 $206.65   13.808%   $235.1842   $235.18   $235.20   $235.20  
  Purchase #6 $124.30   4.517%   $129.9146   $129.91   $129.90   $129.90  
  Purchase #7 $94.88   13.323%   $107.5209   $107.52   $107.50   $107.50  
  7 purchase totals = $1,141.90       $1,253.6694   $1,253.65   $1,253.65   $1,253.70