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 $208.61   11.269%   $232.1183   $232.12   $232.10   $232.10  
  Purchase #2 $43.33   8.312%   $46.9316   $46.93   $46.95   $46.90  
  Purchase #3 $95.86   5.376%   $101.0134   $101.01   $101.00   $101.00  
  Purchase #4 $209.59   9.395%   $229.281   $229.28   $229.30   $229.30  
  Purchase #5 $246.41   10.615%   $272.5664   $272.57   $272.55   $272.60  
  Purchase #6 $96.73   13.801%   $110.0797   $110.08   $110.10   $110.10  
  Purchase #7 $72.37   5.223%   $76.1499   $76.15   $76.15   $76.10  
  7 purchase totals = $972.90       $1,068.1403   $1,068.14   $1,068.15   $1,068.10