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 $123.62   13.570%   $140.3952   $140.40   $140.40   $140.40  
  Purchase #2 $177.92   12.272%   $199.7543   $199.75   $199.75   $199.80  
  Purchase #3 $57.36   7.457%   $61.6373   $61.64   $61.65   $61.60  
  Purchase #4 $110.55   12.658%   $124.5434   $124.54   $124.55   $124.50  
  Purchase #5 $42.96   12.324%   $48.2544   $48.25   $48.25   $48.30  
  Purchase #6 $218.74   3.759%   $226.9624   $226.96   $226.95   $227.00  
  Purchase #7 $249.74   3.617%   $258.7731   $258.77   $258.75   $258.80  
  7 purchase totals = $980.89       $1,060.3201   $1,060.31   $1,060.30   $1,060.40