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 $69.49   7.525%   $74.7191   $74.72   $74.70   $74.70  
  Purchase #2 $19.66   13.202%   $22.2555   $22.26   $22.25   $22.30  
  Purchase #3 $79.87   7.225%   $85.6406   $85.64   $85.65   $85.60  
  Purchase #4 $62.35   7.585%   $67.0792   $67.08   $67.10   $67.10  
  Purchase #5 $202.34   5.272%   $213.0074   $213.01   $213.00   $213.00  
  Purchase #6 $192.81   4.647%   $201.7699   $201.77   $201.75   $201.80  
  Purchase #7 $8.51   5.306%   $8.9615   $8.96   $8.95   $9.00  
  7 purchase totals = $635.03       $673.4332   $673.44   $673.40   $673.50