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 $247.75   11.139%   $275.3469   $275.35   $275.35   $275.30  
  Purchase #2 $49.66   7.826%   $53.5464   $53.55   $53.55   $53.50  
  Purchase #3 $63.65   5.219%   $66.9719   $66.97   $66.95   $67.00  
  Purchase #4 $165.76   12.566%   $186.5894   $186.59   $186.60   $186.60  
  Purchase #5 $76.42   4.281%   $79.6915   $79.69   $79.70   $79.70  
  Purchase #6 $134.35   8.271%   $145.4621   $145.46   $145.45   $145.50  
  Purchase #7 $229.54   4.809%   $240.5786   $240.58   $240.60   $240.60  
  7 purchase totals = $967.13       $1,048.1868   $1,048.19   $1,048.20   $1,048.20