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 $57.55   12.866%   $64.9544   $64.95   $64.95   $65.00  
  Purchase #2 $116.66   4.244%   $121.6111   $121.61   $121.60   $121.60  
  Purchase #3 $105.75   9.765%   $116.0765   $116.08   $116.10   $116.10  
  Purchase #4 $243.51   10.474%   $269.0152   $269.02   $269.00   $269.00  
  Purchase #5 $90.92   7.281%   $97.5399   $97.54   $97.55   $97.50  
  Purchase #6 $176.80   5.632%   $186.7574   $186.76   $186.75   $186.80  
  Purchase #7 $132.48   6.623%   $141.2542   $141.25   $141.25   $141.30  
  7 purchase totals = $923.67       $997.2087   $997.21   $997.20   $997.30