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 $62.26   6.269%   $66.1631   $66.16   $66.15   $66.20  
  Purchase #2 $27.96   4.802%   $29.3026   $29.30   $29.30   $29.30  
  Purchase #3 $216.31   8.768%   $235.2761   $235.28   $235.30   $235.30  
  Purchase #4 $133.26   11.869%   $149.0766   $149.08   $149.10   $149.10  
  Purchase #5 $242.79   9.580%   $266.0493   $266.05   $266.05   $266.00  
  Purchase #6 $71.90   11.454%   $80.1354   $80.14   $80.15   $80.10  
  Purchase #7 $127.73   5.367%   $134.5853   $134.59   $134.60   $134.60  
  7 purchase totals = $882.21       $960.5884   $960.60   $960.65   $960.60