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 $176.43   5.570%   $186.2572   $186.26   $186.25   $186.30  
  Purchase #2 $53.52   12.247%   $60.0746   $60.07   $60.05   $60.10  
  Purchase #3 $115.36   10.485%   $127.4555   $127.46   $127.45   $127.50  
  Purchase #4 $224.65   10.554%   $248.3596   $248.36   $248.35   $248.40  
  Purchase #5 $176.73   10.714%   $195.6649   $195.66   $195.65   $195.70  
  Purchase #6 $10.56   11.572%   $11.782   $11.78   $11.80   $11.80  
  Purchase #7 $178.46   12.686%   $201.0994   $201.10   $201.10   $201.10  
  7 purchase totals = $935.71       $1,030.6932   $1,030.69   $1,030.65   $1,030.90