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 $228.89   11.379%   $254.9354   $254.94   $254.95   $254.90  
  Purchase #2 $239.28   6.295%   $254.3427   $254.34   $254.35   $254.30  
  Purchase #3 $12.82   6.357%   $13.635   $13.64   $13.65   $13.60  
  Purchase #4 $125.32   8.739%   $136.2717   $136.27   $136.25   $136.30  
  Purchase #5 $85.35   6.459%   $90.8628   $90.86   $90.85   $90.90  
  Purchase #6 $226.92   9.510%   $248.5001   $248.50   $248.50   $248.50  
  Purchase #7 $32.52   11.288%   $36.1909   $36.19   $36.20   $36.20  
  7 purchase totals = $951.10       $1,034.7386   $1,034.74   $1,034.75   $1,034.70