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 $240.32   9.852%   $263.9963   $264.00   $264.00   $264.00  
  Purchase #2 $108.33   3.348%   $111.9569   $111.96   $111.95   $112.00  
  Purchase #3 $121.94   11.236%   $135.6412   $135.64   $135.65   $135.60  
  Purchase #4 $157.40   10.860%   $174.4936   $174.49   $174.50   $174.50  
  Purchase #5 $139.68   4.194%   $145.5382   $145.54   $145.55   $145.50  
  Purchase #6 $34.66   10.385%   $38.2594   $38.26   $38.25   $38.30  
  Purchase #7 $182.80   9.191%   $199.6011   $199.60   $199.60   $199.60  
  7 purchase totals = $985.13       $1,069.4867   $1,069.49   $1,069.50   $1,069.50