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 $136.74   10.446%   $151.0239   $151.02   $151.00   $151.00  
  Purchase #2 $219.59   10.790%   $243.2838   $243.28   $243.30   $243.30  
  Purchase #3 $127.25   7.724%   $137.0788   $137.08   $137.10   $137.10  
  Purchase #4 $204.45   12.405%   $229.812   $229.81   $229.80   $229.80  
  Purchase #5 $21.91   6.711%   $23.3804   $23.38   $23.40   $23.40  
  Purchase #6 $67.56   8.826%   $73.5228   $73.52   $73.50   $73.50  
  Purchase #7 $193.61   11.301%   $215.4899   $215.49   $215.50   $215.50  
  7 purchase totals = $971.11       $1,073.5916   $1,073.58   $1,073.60   $1,073.60