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 $163.81   4.315%   $170.8784   $170.88   $170.90   $170.90  
  Purchase #2 $157.71   9.374%   $172.4937   $172.49   $172.50   $172.50  
  Purchase #3 $248.42   11.180%   $276.1934   $276.19   $276.20   $276.20  
  Purchase #4 $206.53   12.306%   $231.9456   $231.95   $231.95   $231.90  
  Purchase #5 $24.72   12.286%   $27.7571   $27.76   $27.75   $27.80  
  Purchase #6 $7.42   11.593%   $8.2802   $8.28   $8.30   $8.30  
  Purchase #7 $43.88   7.186%   $47.0332   $47.03   $47.05   $47.00  
  7 purchase totals = $852.49       $934.5816   $934.58   $934.65   $934.60