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 $229.52   10.646%   $253.9547   $253.95   $253.95   $254.00  
  Purchase #2 $37.37   11.523%   $41.6761   $41.68   $41.70   $41.70  
  Purchase #3 $57.60   12.409%   $64.7476   $64.75   $64.75   $64.70  
  Purchase #4 $229.30   8.212%   $248.1301   $248.13   $248.15   $248.10  
  Purchase #5 $237.91   13.437%   $269.878   $269.88   $269.90   $269.90  
  Purchase #6 $137.81   12.516%   $155.0583   $155.06   $155.05   $155.10  
  Purchase #7 $43.37   6.427%   $46.1574   $46.16   $46.15   $46.20  
  7 purchase totals = $972.88       $1,079.6022   $1,079.61   $1,079.65   $1,079.70