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 $145.48   5.851%   $153.992   $153.99   $154.00   $154.00  
  Purchase #2 $198.93   11.582%   $221.9701   $221.97   $221.95   $222.00  
  Purchase #3 $103.90   9.540%   $113.8121   $113.81   $113.80   $113.80  
  Purchase #4 $244.62   11.638%   $273.0889   $273.09   $273.10   $273.10  
  Purchase #5 $86.98   10.311%   $95.9485   $95.95   $95.95   $95.90  
  Purchase #6 $174.50   12.595%   $196.4783   $196.48   $196.50   $196.50  
  Purchase #7 $153.38   11.395%   $170.8577   $170.86   $170.85   $170.90  
  7 purchase totals = $1,107.79       $1,226.1476   $1,226.15   $1,226.15   $1,226.20