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 $84.30   13.436%   $95.6265   $95.63   $95.65   $95.60  
  Purchase #2 $24.82   9.196%   $27.1024   $27.10   $27.10   $27.10  
  Purchase #3 $209.35   13.374%   $237.3485   $237.35   $237.35   $237.30  
  Purchase #4 $124.28   4.720%   $130.146   $130.15   $130.15   $130.10  
  Purchase #5 $47.43   5.736%   $50.1506   $50.15   $50.15   $50.20  
  Purchase #6 $170.47   7.660%   $183.528   $183.53   $183.55   $183.50  
  Purchase #7 $118.32   13.771%   $134.6138   $134.61   $134.60   $134.60  
  7 purchase totals = $778.97       $858.5158   $858.52   $858.55   $858.40