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 $241.64   10.799%   $267.7347   $267.73   $267.75   $267.70  
  Purchase #2 $122.61   11.864%   $137.1565   $137.16   $137.15   $137.20  
  Purchase #3 $161.30   13.388%   $182.8948   $182.89   $182.90   $182.90  
  Purchase #4 $113.92   7.824%   $122.8331   $122.83   $122.85   $122.80  
  Purchase #5 $192.52   7.510%   $206.9783   $206.98   $207.00   $207.00  
  Purchase #6 $65.38   13.353%   $74.1102   $74.11   $74.10   $74.10  
  Purchase #7 $175.89   9.577%   $192.735   $192.74   $192.75   $192.70  
  7 purchase totals = $1,073.26       $1,184.4426   $1,184.44   $1,184.50   $1,184.40