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 $219.64   13.486%   $249.2607   $249.26   $249.25   $249.30  
  Purchase #2 $151.68   12.453%   $170.5687   $170.57   $170.55   $170.60  
  Purchase #3 $118.54   7.799%   $127.7849   $127.78   $127.80   $127.80  
  Purchase #4 $147.60   4.735%   $154.5889   $154.59   $154.60   $154.60  
  Purchase #5 $22.40   6.447%   $23.8441   $23.84   $23.85   $23.80  
  Purchase #6 $172.78   11.869%   $193.2873   $193.29   $193.30   $193.30  
  Purchase #7 $191.64   7.657%   $206.3139   $206.31   $206.30   $206.30  
  7 purchase totals = $1,024.28       $1,125.6485   $1,125.64   $1,125.65   $1,125.70