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 $244.36   5.569%   $257.9684   $257.97   $257.95   $258.00  
  Purchase #2 $52.79   7.803%   $56.9092   $56.91   $56.90   $56.90  
  Purchase #3 $203.68   4.863%   $213.585   $213.59   $213.60   $213.60  
  Purchase #4 $227.99   5.157%   $239.7474   $239.75   $239.75   $239.70  
  Purchase #5 $239.66   13.293%   $271.518   $271.52   $271.50   $271.50  
  Purchase #6 $67.96   12.576%   $76.5066   $76.51   $76.50   $76.50  
  Purchase #7 $243.71   11.108%   $270.7813   $270.78   $270.80   $270.80  
  7 purchase totals = $1,280.15       $1,387.0159   $1,387.03   $1,387.00   $1,387.00