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 $147.36   13.853%   $167.7738   $167.77   $167.75   $167.80  
  Purchase #2 $226.71   5.841%   $239.9521   $239.95   $239.95   $240.00  
  Purchase #3 $214.41   12.780%   $241.8116   $241.81   $241.80   $241.80  
  Purchase #4 $219.44   13.569%   $249.2158   $249.22   $249.20   $249.20  
  Purchase #5 $45.25   13.864%   $51.5235   $51.52   $51.50   $51.50  
  Purchase #6 $110.38   6.629%   $117.6971   $117.70   $117.70   $117.70  
  Purchase #7 $32.55   13.318%   $36.885   $36.89   $36.90   $36.90  
  7 purchase totals = $996.10       $1,104.8589   $1,104.86   $1,104.80   $1,104.90