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 $148.47   12.849%   $167.5469   $167.55   $167.55   $167.50  
  Purchase #2 $239.61   5.421%   $252.5993   $252.60   $252.60   $252.60  
  Purchase #3 $235.41   7.567%   $253.2235   $253.22   $253.20   $253.20  
  Purchase #4 $30.48   5.222%   $32.0717   $32.07   $32.05   $32.10  
  Purchase #5 $182.32   10.305%   $201.1081   $201.11   $201.10   $201.10  
  Purchase #6 $249.28   5.618%   $263.2846   $263.28   $263.30   $263.30  
  Purchase #7 $243.84   9.500%   $267.0048   $267.00   $267.00   $267.00  
  7 purchase totals = $1,329.41       $1,436.8389   $1,436.83   $1,436.80   $1,436.80