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 $92.38   5.822%   $97.7584   $97.76   $97.75   $97.80  
  Purchase #2 $211.55   9.228%   $231.0718   $231.07   $231.05   $231.10  
  Purchase #3 $165.97   6.343%   $176.4975   $176.50   $176.50   $176.50  
  Purchase #4 $100.97   6.755%   $107.7905   $107.79   $107.80   $107.80  
  Purchase #5 $130.82   3.367%   $135.2247   $135.22   $135.20   $135.20  
  Purchase #6 $102.54   12.371%   $115.2252   $115.23   $115.25   $115.20  
  Purchase #7 $162.58   13.816%   $185.0421   $185.04   $185.05   $185.00  
  7 purchase totals = $966.81       $1,048.6102   $1,048.61   $1,048.60   $1,048.60