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 $60.52   13.408%   $68.6345   $68.63   $68.65   $68.60  
  Purchase #2 $198.54   3.304%   $205.0998   $205.10   $205.10   $205.10  
  Purchase #3 $230.61   11.862%   $257.965   $257.97   $257.95   $258.00  
  Purchase #4 $223.71   6.336%   $237.8843   $237.88   $237.90   $237.90  
  Purchase #5 $49.83   5.448%   $52.5447   $52.54   $52.55   $52.50  
  Purchase #6 $19.60   10.332%   $21.6251   $21.63   $21.65   $21.60  
  Purchase #7 $133.84   5.701%   $141.4702   $141.47   $141.45   $141.50  
  7 purchase totals = $916.65       $985.2236   $985.22   $985.25   $985.20