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 $243.60   7.681%   $262.3109   $262.31   $262.30   $262.30  
  Purchase #2 $174.69   4.298%   $182.1982   $182.20   $182.20   $182.20  
  Purchase #3 $165.50   13.589%   $187.9898   $187.99   $188.00   $188.00  
  Purchase #4 $114.38   4.642%   $119.6895   $119.69   $119.70   $119.70  
  Purchase #5 $168.55   9.223%   $184.0954   $184.10   $184.10   $184.10  
  Purchase #6 $112.65   7.107%   $120.656   $120.66   $120.65   $120.70  
  Purchase #7 $250.40   11.567%   $279.3638   $279.36   $279.35   $279.40  
  7 purchase totals = $1,229.77       $1,336.3036   $1,336.31   $1,336.30   $1,336.40