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 $238.56   3.524%   $246.9669   $246.97   $246.95   $247.00  
  Purchase #2 $82.52   13.301%   $93.496   $93.50   $93.50   $93.50  
  Purchase #3 $65.48   4.715%   $68.5674   $68.57   $68.55   $68.60  
  Purchase #4 $62.71   9.557%   $68.7032   $68.70   $68.70   $68.70  
  Purchase #5 $75.70   9.638%   $82.996   $83.00   $83.00   $83.00  
  Purchase #6 $229.78   4.195%   $239.4193   $239.42   $239.40   $239.40  
  Purchase #7 $228.32   5.765%   $241.4826   $241.48   $241.50   $241.50  
  7 purchase totals = $983.07       $1,041.6314   $1,041.64   $1,041.60   $1,041.70