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 $54.60   13.255%   $61.8372   $61.84   $61.85   $61.80  
  Purchase #2 $124.78   13.367%   $141.4593   $141.46   $141.45   $141.50  
  Purchase #3 $32.37   5.380%   $34.1115   $34.11   $34.10   $34.10  
  Purchase #4 $108.28   6.675%   $115.5077   $115.51   $115.50   $115.50  
  Purchase #5 $141.90   9.713%   $155.6827   $155.68   $155.70   $155.70  
  Purchase #6 $116.90   3.489%   $120.9786   $120.98   $121.00   $121.00  
  Purchase #7 $222.80   8.376%   $241.4617   $241.46   $241.45   $241.50  
  7 purchase totals = $801.63       $871.0387   $871.04   $871.05   $871.10