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 $192.48   13.113%   $217.7199   $217.72   $217.70   $217.70  
  Purchase #2 $234.96   3.836%   $243.9731   $243.97   $243.95   $244.00  
  Purchase #3 $55.37   11.606%   $61.7962   $61.80   $61.80   $61.80  
  Purchase #4 $198.44   3.749%   $205.8795   $205.88   $205.90   $205.90  
  Purchase #5 $87.99   4.117%   $91.6125   $91.61   $91.60   $91.60  
  Purchase #6 $46.98   7.216%   $50.3701   $50.37   $50.35   $50.40  
  Purchase #7 $149.64   7.650%   $161.0875   $161.09   $161.10   $161.10  
  7 purchase totals = $965.86       $1,032.4388   $1,032.44   $1,032.40   $1,032.50