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 $54.33   11.825%   $60.7545   $60.75   $60.75   $60.80  
  Purchase #2 $54.82   10.754%   $60.7153   $60.72   $60.70   $60.70  
  Purchase #3 $130.59   4.120%   $135.9703   $135.97   $135.95   $136.00  
  Purchase #4 $192.45   9.735%   $211.185   $211.19   $211.20   $211.20  
  Purchase #5 $186.95   8.621%   $203.067   $203.07   $203.05   $203.10  
  Purchase #6 $136.88   11.716%   $152.9169   $152.92   $152.90   $152.90  
  Purchase #7 $212.69   12.511%   $239.2996   $239.30   $239.30   $239.30  
  7 purchase totals = $968.71       $1,063.9086   $1,063.92   $1,063.85   $1,064.00