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 $86.59   8.657%   $94.0861   $94.09   $94.10   $94.10  
  Purchase #2 $209.53   12.311%   $235.3252   $235.33   $235.35   $235.30  
  Purchase #3 $188.60   11.836%   $210.9227   $210.92   $210.90   $210.90  
  Purchase #4 $186.47   6.432%   $198.4638   $198.46   $198.45   $198.50  
  Purchase #5 $229.27   13.307%   $259.779   $259.78   $259.80   $259.80  
  Purchase #6 $49.52   5.560%   $52.2733   $52.27   $52.25   $52.30  
  Purchase #7 $186.27   3.619%   $193.0111   $193.01   $193.00   $193.00  
  7 purchase totals = $1,136.25       $1,243.8612   $1,243.86   $1,243.85   $1,243.90