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 $48.77   11.648%   $54.4507   $54.45   $54.45   $54.50  
  Purchase #2 $62.93   13.372%   $71.345   $71.35   $71.35   $71.30  
  Purchase #3 $70.60   12.114%   $79.1525   $79.15   $79.15   $79.20  
  Purchase #4 $174.57   10.711%   $193.2682   $193.27   $193.25   $193.30  
  Purchase #5 $9.91   11.786%   $11.078   $11.08   $11.10   $11.10  
  Purchase #6 $135.70   9.122%   $148.0786   $148.08   $148.10   $148.10  
  Purchase #7 $192.66   8.304%   $208.6585   $208.66   $208.65   $208.70  
  7 purchase totals = $695.14       $766.0315   $766.04   $766.05   $766.20