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 $238.52   3.567%   $247.028   $247.03   $247.05   $247.00  
  Purchase #2 $213.65   9.779%   $234.5428   $234.54   $234.55   $234.50  
  Purchase #3 $117.95   8.267%   $127.7009   $127.70   $127.70   $127.70  
  Purchase #4 $166.93   6.284%   $177.4199   $177.42   $177.40   $177.40  
  Purchase #5 $149.97   6.583%   $159.8425   $159.84   $159.85   $159.80  
  Purchase #6 $59.91   13.685%   $68.1087   $68.11   $68.10   $68.10  
  Purchase #7 $23.88   11.442%   $26.6123   $26.61   $26.60   $26.60  
  7 purchase totals = $970.81       $1,041.2551   $1,041.25   $1,041.25   $1,041.10